diff --git a/components/servo/Cargo.lock b/components/servo/Cargo.lock
index 211f46106eed..6b99146dee02 100644
--- a/components/servo/Cargo.lock
+++ b/components/servo/Cargo.lock
@@ -46,8 +46,8 @@ dependencies = [
  "util 0.0.1",
  "util_tests 0.0.1",
  "webdriver_server 0.0.1",
- "webrender 0.7.0 (git+https://github.com/servo/webrender)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender 0.8.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -233,7 +233,7 @@ dependencies = [
  "offscreen_gl_context 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "plugins 0.0.1",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -250,7 +250,7 @@ dependencies = [
  "plugins 0.0.1",
  "serde 0.8.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.8.12 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -338,8 +338,8 @@ dependencies = [
  "time 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender 0.7.0 (git+https://github.com/servo/webrender)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender 0.8.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -370,7 +370,7 @@ dependencies = [
  "style_traits 0.0.1",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -815,7 +815,7 @@ dependencies = [
  "unicode-script 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "xi-unicode 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1166,7 +1166,7 @@ dependencies = [
  "unicode-script 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1205,7 +1205,7 @@ dependencies = [
  "style 0.0.1",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1219,7 +1219,7 @@ dependencies = [
  "profile_traits 0.0.1",
  "script_traits 0.0.1",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1388,7 +1388,7 @@ dependencies = [
  "plugins 0.0.1",
  "serde 0.8.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.8.12 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1426,7 +1426,7 @@ dependencies = [
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "uuid 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1484,7 +1484,7 @@ dependencies = [
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "uuid 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1989,7 +1989,7 @@ dependencies = [
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "uuid 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "xml5ever 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -2666,8 +2666,8 @@ dependencies = [
 
 [[package]]
 name = "webrender"
-version = "0.7.0"
-source = "git+https://github.com/servo/webrender#4440d1daa3d6e9630d4b164f7bae644b9dc4cb8a"
+version = "0.8.0"
+source = "git+https://github.com/servo/webrender#d44b1ffd3ea9e9e97ef7a70c1ac0f53bbd626850"
 dependencies = [
  "app_units 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2686,13 +2686,13 @@ dependencies = [
  "offscreen_gl_context 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
 name = "webrender_traits"
-version = "0.7.0"
-source = "git+https://github.com/servo/webrender#4440d1daa3d6e9630d4b164f7bae644b9dc4cb8a"
+version = "0.8.0"
+source = "git+https://github.com/servo/webrender#d44b1ffd3ea9e9e97ef7a70c1ac0f53bbd626850"
 dependencies = [
  "app_units 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3009,8 +3009,8 @@ dependencies = [
 "checksum wayland-sys 0.5.11 (registry+https://github.com/rust-lang/crates.io-index)" = "9633f7fe5de56544215f82eaf1b76bf1b584becf7f08b58cbef4c2c7d10e803a"
 "checksum wayland-window 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "309b69d3a863c9c21422d889fb7d98cf02f8a2ca054960a49243ce5b67ad884c"
 "checksum webdriver 0.14.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ee2d66e90672022ced375134329c57be4db228b19b120b97b744a469c381be06"
-"checksum webrender 0.7.0 (git+https://github.com/servo/webrender)" = "<none>"
-"checksum webrender_traits 0.7.0 (git+https://github.com/servo/webrender)" = "<none>"
+"checksum webrender 0.8.0 (git+https://github.com/servo/webrender)" = "<none>"
+"checksum webrender_traits 0.8.0 (git+https://github.com/servo/webrender)" = "<none>"
 "checksum websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)" = "bb4a1a6ea5ed0367f32eb3d94dcc58859ef4294b5f75ba983dbf56ac314af45d"
 "checksum winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)" = "167dc9d6949a9b857f3451275e911c3f44255842c1f7a76f33c55103a909087a"
 "checksum winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2d315eee3b34aca4797b2da6b13ed88266e6d612562a0c46390af8299fc699bc"
diff --git a/ports/cef/Cargo.lock b/ports/cef/Cargo.lock
index 1e44021bfbfd..835d008f4f32 100644
--- a/ports/cef/Cargo.lock
+++ b/ports/cef/Cargo.lock
@@ -206,7 +206,7 @@ dependencies = [
  "offscreen_gl_context 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "plugins 0.0.1",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -223,7 +223,7 @@ dependencies = [
  "plugins 0.0.1",
  "serde 0.8.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.8.12 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -295,8 +295,8 @@ dependencies = [
  "time 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender 0.7.0 (git+https://github.com/servo/webrender)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender 0.8.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -327,7 +327,7 @@ dependencies = [
  "style_traits 0.0.1",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -731,7 +731,7 @@ dependencies = [
  "unicode-script 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "xi-unicode 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1073,7 +1073,7 @@ dependencies = [
  "unicode-script 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1105,7 +1105,7 @@ dependencies = [
  "style 0.0.1",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1119,7 +1119,7 @@ dependencies = [
  "profile_traits 0.0.1",
  "script_traits 0.0.1",
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1288,7 +1288,7 @@ dependencies = [
  "plugins 0.0.1",
  "serde 0.8.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.8.12 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -1326,7 +1326,7 @@ dependencies = [
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "uuid 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1362,7 +1362,7 @@ dependencies = [
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "uuid 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1840,7 +1840,7 @@ dependencies = [
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "uuid 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
  "websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "xml5ever 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1998,8 +1998,8 @@ dependencies = [
  "url 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "webdriver_server 0.0.1",
- "webrender 0.7.0 (git+https://github.com/servo/webrender)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender 0.8.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
@@ -2524,8 +2524,8 @@ dependencies = [
 
 [[package]]
 name = "webrender"
-version = "0.7.0"
-source = "git+https://github.com/servo/webrender#4440d1daa3d6e9630d4b164f7bae644b9dc4cb8a"
+version = "0.8.0"
+source = "git+https://github.com/servo/webrender#d44b1ffd3ea9e9e97ef7a70c1ac0f53bbd626850"
 dependencies = [
  "app_units 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2544,13 +2544,13 @@ dependencies = [
  "offscreen_gl_context 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
- "webrender_traits 0.7.0 (git+https://github.com/servo/webrender)",
+ "webrender_traits 0.8.0 (git+https://github.com/servo/webrender)",
 ]
 
 [[package]]
 name = "webrender_traits"
-version = "0.7.0"
-source = "git+https://github.com/servo/webrender#4440d1daa3d6e9630d4b164f7bae644b9dc4cb8a"
+version = "0.8.0"
+source = "git+https://github.com/servo/webrender#d44b1ffd3ea9e9e97ef7a70c1ac0f53bbd626850"
 dependencies = [
  "app_units 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2861,8 +2861,8 @@ dependencies = [
 "checksum wayland-sys 0.5.11 (registry+https://github.com/rust-lang/crates.io-index)" = "9633f7fe5de56544215f82eaf1b76bf1b584becf7f08b58cbef4c2c7d10e803a"
 "checksum wayland-window 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "309b69d3a863c9c21422d889fb7d98cf02f8a2ca054960a49243ce5b67ad884c"
 "checksum webdriver 0.14.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ee2d66e90672022ced375134329c57be4db228b19b120b97b744a469c381be06"
-"checksum webrender 0.7.0 (git+https://github.com/servo/webrender)" = "<none>"
-"checksum webrender_traits 0.7.0 (git+https://github.com/servo/webrender)" = "<none>"
+"checksum webrender 0.8.0 (git+https://github.com/servo/webrender)" = "<none>"
+"checksum webrender_traits 0.8.0 (git+https://github.com/servo/webrender)" = "<none>"
 "checksum websocket 0.17.1 (registry+https://github.com/rust-lang/crates.io-index)" = "bb4a1a6ea5ed0367f32eb3d94dcc58859ef4294b5f75ba983dbf56ac314af45d"
 "checksum winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)" = "167dc9d6949a9b857f3451275e911c3f44255842c1f7a76f33c55103a909087a"
 "checksum winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2d315eee3b34aca4797b2da6b13ed88266e6d612562a0c46390af8299fc699bc"
diff --git a/resources/shaders/cs_box_shadow.fs.glsl b/resources/shaders/cs_box_shadow.fs.glsl
new file mode 100644
index 000000000000..3243dc6d6284
--- /dev/null
+++ b/resources/shaders/cs_box_shadow.fs.glsl
@@ -0,0 +1,148 @@
+#line 1
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// See http://asciimath.org to render the equations here.
+
+// The Gaussian function used for blurring:
+//
+//     G_sigma(x) = 1/sqrt(2 pi sigma^2) e^(-x^2/(2 sigma^2))
+float gauss(float x, float sigma) {
+    float sigmaPow2 = sigma * sigma;
+    return 1.0 / sqrt(6.283185307179586 * sigmaPow2) * exp(-(x * x) / (2.0 * sigmaPow2));
+}
+
+// An approximation of the error function, which is related to the integral of the Gaussian
+// function:
+//
+//     "erf"(x) = 2/sqrt(pi) int_0^x e^(-t^2) dt
+//              ~~ 1 - 1 / (1 + a_1 x + a_2 x^2 + a_3 x^3 + a_4 x^4)^4
+//
+// where:
+//
+//     a_1 = 0.278393, a_2 = 0.230389, a_3 = 0.000972, a_4 = 0.078108
+//
+// This approximation is accurate to `5 xx 10^-4`, more than accurate enough for our purposes.
+//
+// See: https://en.wikipedia.org/wiki/Error_function#Approximation_with_elementary_functions
+float erf(float x) {
+    bool negative = x < 0.0;
+    if (negative)
+        x = -x;
+    float x2 = x * x;
+    float x3 = x2 * x;
+    float x4 = x2 * x2;
+    float denom = 1.0 + 0.278393 * x + 0.230389 * x2 + 0.000972 * x3 + 0.078108 * x4;
+    float result = 1.0 - 1.0 / (denom * denom * denom * denom);
+    return negative ? -result : result;
+}
+
+// A useful helper for calculating integrals of the Gaussian function via the error function:
+//
+//      "erf"_sigma(x) = 2 int 1/sqrt(2 pi sigma^2) e^(-x^2/(2 sigma^2)) dx
+//                     = "erf"(x/(sigma sqrt(2)))
+float erfSigma(float x, float sigma) {
+    return erf(x / (sigma * 1.4142135623730951));
+}
+
+// Returns the blurred color value from the box itself (not counting any rounded corners). `p_0` is
+// the vector distance to the top left corner of the box; `p_1` is the vector distance to its
+// bottom right corner.
+//
+//      "colorFromRect"_sigma(p_0, p_1)
+//          = int_{p_{0_y}}^{p_{1_y}} int_{p_{1_x}}^{p_{0_x}} G_sigma(y) G_sigma(x) dx dy
+//          = 1/4 ("erf"_sigma(p_{1_x}) - "erf"_sigma(p_{0_x}))
+//              ("erf"_sigma(p_{1_y}) - "erf"_sigma(p_{0_y}))
+float colorFromRect(vec2 p0, vec2 p1, float sigma) {
+    return (erfSigma(p1.x, sigma) - erfSigma(p0.x, sigma)) *
+        (erfSigma(p1.y, sigma) - erfSigma(p0.y, sigma)) / 4.0;
+}
+
+// Returns the `x` coordinate on the ellipse with the given radii for the given `y` coordinate:
+//
+//      "ellipsePoint"(y, y_0, a, b) = a sqrt(1 - ((y - y_0) / b)^2)
+float ellipsePoint(float y, float y0, vec2 radii) {
+    float bStep = (y - y0) / radii.y;
+    return radii.x * sqrt(1.0 - bStep * bStep);
+}
+
+// A helper function to compute the value that needs to be subtracted to accommodate the border
+// corners.
+//
+//     "colorCutout"_sigma(x_{0_l}, x_{0_r}, y_0, y_{min}, y_{max}, a, b)
+//          = int_{y_{min}}^{y_{max}}
+//              int_{x_{0_r} + "ellipsePoint"(y, y_0, a, b)}^{x_{0_r} + a} G_sigma(y) G_sigma(x) dx
+//              + int_{x_{0_l} - a}^{x_{0_l} - "ellipsePoint"(y, y_0, a, b)} G_sigma(y) G_sigma(x)
+//                  dx dy
+//          = int_{y_{min}}^{y_{max}} 1/2 G_sigma(y)
+//              ("erf"_sigma(x_{0_r} + a) - "erf"_sigma(x_{0_r} + "ellipsePoint"(y, y_0, a, b)) +
+//               "erf"_sigma(x_{0_l} - "ellipsePoint"(y, y_0, a, b)) - "erf"_sigma(x_{0_l} - a))
+//
+// with the outer integral evaluated numerically.
+float colorCutoutGeneral(float x0l,
+                         float x0r,
+                         float y0,
+                         float yMin,
+                         float yMax,
+                         vec2 radii,
+                         float sigma) {
+    float sum = 0.0;
+    for (float y = yMin; y <= yMax; y += 1.0) {
+        float xEllipsePoint = ellipsePoint(y, y0, radii);
+        sum += gauss(y, sigma) *
+            (erfSigma(x0r + radii.x, sigma) - erfSigma(x0r + xEllipsePoint, sigma) +
+             erfSigma(x0l - xEllipsePoint, sigma) - erfSigma(x0l - radii.x, sigma));
+    }
+    return sum / 2.0;
+}
+
+// The value that needs to be subtracted to accommodate the top border corners.
+float colorCutoutTop(float x0l, float x0r, float y0, vec2 radii, float sigma) {
+    return colorCutoutGeneral(x0l, x0r, y0, y0, y0 + radii.y, radii, sigma);
+}
+
+// The value that needs to be subtracted to accommodate the bottom border corners.
+float colorCutoutBottom(float x0l, float x0r, float y0, vec2 radii, float sigma) {
+    return colorCutoutGeneral(x0l, x0r, y0, y0 - radii.y, y0, radii, sigma);
+}
+
+// The blurred color value for the point at `pos` with the top left corner of the box at
+// `p_{0_"rect"}` and the bottom right corner of the box at `p_{1_"rect"}`.
+float color(vec2 pos, vec2 p0Rect, vec2 p1Rect, vec2 radii, float sigma) {
+    // Compute the vector distances `p_0` and `p_1`.
+    vec2 p0 = p0Rect - pos, p1 = p1Rect - pos;
+
+    // Compute the basic color `"colorFromRect"_sigma(p_0, p_1)`. This is all we have to do if
+    // the box is unrounded.
+    float cRect = colorFromRect(p0, p1, sigma);
+    if (radii.x == 0.0 || radii.y == 0.0)
+        return cRect;
+
+    // Compute the inner corners of the box, taking border radii into account: `x_{0_l}`,
+    // `y_{0_t}`, `x_{0_r}`, and `y_{0_b}`.
+    float x0l = p0.x + radii.x;
+    float y0t = p1.y - radii.y;
+    float x0r = p1.x - radii.x;
+    float y0b = p0.y + radii.y;
+
+    // Compute the final color:
+    //
+    //     "colorFromRect"_sigma(p_0, p_1) -
+    //          ("colorCutoutTop"_sigma(x_{0_l}, x_{0_r}, y_{0_t}, a, b) +
+    //           "colorCutoutBottom"_sigma(x_{0_l}, x_{0_r}, y_{0_b}, a, b))
+    float cCutoutTop = colorCutoutTop(x0l, x0r, y0t, radii, sigma);
+    float cCutoutBottom = colorCutoutBottom(x0l, x0r, y0b, radii, sigma);
+    return cRect - (cCutoutTop + cCutoutBottom);
+}
+
+void main(void) {
+    vec2 pos = vPos.xy;
+    vec2 p0Rect = vBoxShadowRect.xy, p1Rect = vBoxShadowRect.zw;
+    vec2 radii = vBorderRadii.xy;
+    float sigma = vBlurRadius / 2.0;
+    float value = color(pos, p0Rect, p1Rect, radii, sigma);
+
+    value = max(value, 0.0);
+    oFragColor = vec4(1.0, 1.0, 1.0, vInverted == 1.0 ? 1.0 - value : value);
+}
diff --git a/resources/shaders/cs_box_shadow.glsl b/resources/shaders/cs_box_shadow.glsl
new file mode 100644
index 000000000000..9e5dd036c542
--- /dev/null
+++ b/resources/shaders/cs_box_shadow.glsl
@@ -0,0 +1,10 @@
+#line 1
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+varying vec2 vPos;
+flat varying vec2 vBorderRadii;
+flat varying float vBlurRadius;
+flat varying vec4 vBoxShadowRect;
+flat varying float vInverted;
diff --git a/resources/shaders/cs_box_shadow.vs.glsl b/resources/shaders/cs_box_shadow.vs.glsl
new file mode 100644
index 000000000000..fce6e53af1d6
--- /dev/null
+++ b/resources/shaders/cs_box_shadow.vs.glsl
@@ -0,0 +1,31 @@
+#line 1
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+void main(void) {
+    CachePrimitiveInstance cpi = fetch_cache_instance(gl_InstanceID);
+    RenderTaskData task = fetch_render_task(cpi.render_task_index);
+    BoxShadow bs = fetch_boxshadow(cpi.specific_prim_index);
+
+    vec2 p0 = task.data0.xy;
+    vec2 p1 = p0 + task.data0.zw;
+
+    vec2 pos = mix(p0, p1, aPosition.xy);
+
+    vBorderRadii = bs.border_radius_edge_size_blur_radius_inverted.xx;
+    vBlurRadius = bs.border_radius_edge_size_blur_radius_inverted.z;
+    vInverted = bs.border_radius_edge_size_blur_radius_inverted.w;
+    vBoxShadowRect = vec4(bs.bs_rect.xy, bs.bs_rect.xy + bs.bs_rect.zw);
+
+    // The fragment shader expects logical units, beginning at where the
+    // blur radius begins.
+    // The first path of the equation gets the virtual position in
+    // logical pixels within the patch rectangle (accounting for
+    // bilinear offset). Then we add the start position of the
+    // box shadow rect and subtract the blur radius to get the
+    // virtual coordinates that the FS expects.
+    vPos = (pos - 1.0 - p0) / uDevicePixelRatio + bs.bs_rect.xy - vec2(2.0 * vBlurRadius);
+
+    gl_Position = uTransform * vec4(pos, 0.0, 1.0);
+}
diff --git a/resources/shaders/prim_shared.glsl b/resources/shaders/prim_shared.glsl
index d25b7152540b..6d6b04e58148 100644
--- a/resources/shaders/prim_shared.glsl
+++ b/resources/shaders/prim_shared.glsl
@@ -39,7 +39,7 @@ uniform sampler2DArray sCache;
 #ifdef WR_VERTEX_SHADER
 
 #define VECS_PER_LAYER             13
-#define VECS_PER_TILE               2
+#define VECS_PER_RENDER_TASK        2
 #define VECS_PER_PRIM_GEOM          2
 
 #define GRADIENT_HORIZONTAL     0
@@ -121,18 +121,33 @@ Layer fetch_layer(int index) {
     return layer;
 }
 
+struct RenderTaskData {
+    vec4 data0;
+    vec4 data1;
+};
+
+RenderTaskData fetch_render_task(int index) {
+    RenderTaskData task;
+
+    ivec2 uv = get_fetch_uv(index, VECS_PER_RENDER_TASK);
+
+    task.data0 = texelFetchOffset(sRenderTasks, uv, 0, ivec2(0, 0));
+    task.data1 = texelFetchOffset(sRenderTasks, uv, 0, ivec2(1, 0));
+
+    return task;
+}
+
 struct Tile {
     vec4 screen_origin_task_origin;
     vec4 size_target_index;
 };
 
 Tile fetch_tile(int index) {
-    Tile tile;
-
-    ivec2 uv = get_fetch_uv(index, VECS_PER_TILE);
+    RenderTaskData task = fetch_render_task(index);
 
-    tile.screen_origin_task_origin = texelFetchOffset(sRenderTasks, uv, 0, ivec2(0, 0));
-    tile.size_target_index = texelFetchOffset(sRenderTasks, uv, 0, ivec2(1, 0));
+    Tile tile;
+    tile.screen_origin_task_origin = task.data0;
+    tile.size_target_index = task.data1;
 
     return tile;
 }
@@ -259,6 +274,27 @@ PrimitiveInstance fetch_instance(int index) {
 
     return pi;
 }
+
+struct CachePrimitiveInstance {
+    int global_prim_index;
+    int specific_prim_index;
+    int render_task_index;
+};
+
+CachePrimitiveInstance fetch_cache_instance(int index) {
+    CachePrimitiveInstance cpi;
+
+    int offset = index * 1;
+
+    ivec4 data0 = int_data[offset + 0];
+
+    cpi.global_prim_index = data0.x;
+    cpi.specific_prim_index = data0.y;
+    cpi.render_task_index = data0.z;
+
+    return cpi;
+}
+
 struct Primitive {
     Layer layer;
     Tile tile;
@@ -553,7 +589,7 @@ struct BoxShadow {
     vec4 src_rect;
     vec4 bs_rect;
     vec4 color;
-    vec4 border_radii_blur_radius_inverted;
+    vec4 border_radius_edge_size_blur_radius_inverted;
 };
 
 BoxShadow fetch_boxshadow(int index) {
@@ -564,7 +600,7 @@ BoxShadow fetch_boxshadow(int index) {
     bs.src_rect = texelFetchOffset(sData64, uv, 0, ivec2(0, 0));
     bs.bs_rect = texelFetchOffset(sData64, uv, 0, ivec2(1, 0));
     bs.color = texelFetchOffset(sData64, uv, 0, ivec2(2, 0));
-    bs.border_radii_blur_radius_inverted = texelFetchOffset(sData64, uv, 0, ivec2(3, 0));
+    bs.border_radius_edge_size_blur_radius_inverted = texelFetchOffset(sData64, uv, 0, ivec2(3, 0));
 
     return bs;
 }
diff --git a/resources/shaders/ps_box_shadow.fs.glsl b/resources/shaders/ps_box_shadow.fs.glsl
index 9c485cba9fed..8392ab698beb 100644
--- a/resources/shaders/ps_box_shadow.fs.glsl
+++ b/resources/shaders/ps_box_shadow.fs.glsl
@@ -2,150 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-// See http://asciimath.org to render the equations here.
-
-// The Gaussian function used for blurring:
-//
-//     G_sigma(x) = 1/sqrt(2 pi sigma^2) e^(-x^2/(2 sigma^2))
-float gauss(float x, float sigma) {
-    float sigmaPow2 = sigma * sigma;
-    return 1.0 / sqrt(6.283185307179586 * sigmaPow2) * exp(-(x * x) / (2.0 * sigmaPow2));
-}
-
-// An approximation of the error function, which is related to the integral of the Gaussian
-// function:
-//
-//     "erf"(x) = 2/sqrt(pi) int_0^x e^(-t^2) dt
-//              ~~ 1 - 1 / (1 + a_1 x + a_2 x^2 + a_3 x^3 + a_4 x^4)^4
-//
-// where:
-//
-//     a_1 = 0.278393, a_2 = 0.230389, a_3 = 0.000972, a_4 = 0.078108
-//
-// This approximation is accurate to `5 xx 10^-4`, more than accurate enough for our purposes.
-//
-// See: https://en.wikipedia.org/wiki/Error_function#Approximation_with_elementary_functions
-float erf(float x) {
-    bool negative = x < 0.0;
-    if (negative)
-        x = -x;
-    float x2 = x * x;
-    float x3 = x2 * x;
-    float x4 = x2 * x2;
-    float denom = 1.0 + 0.278393 * x + 0.230389 * x2 + 0.000972 * x3 + 0.078108 * x4;
-    float result = 1.0 - 1.0 / (denom * denom * denom * denom);
-    return negative ? -result : result;
-}
-
-// A useful helper for calculating integrals of the Gaussian function via the error function:
-//
-//      "erf"_sigma(x) = 2 int 1/sqrt(2 pi sigma^2) e^(-x^2/(2 sigma^2)) dx
-//                     = "erf"(x/(sigma sqrt(2)))
-float erfSigma(float x, float sigma) {
-    return erf(x / (sigma * 1.4142135623730951));
-}
-
-// Returns the blurred color value from the box itself (not counting any rounded corners). `p_0` is
-// the vector distance to the top left corner of the box; `p_1` is the vector distance to its
-// bottom right corner.
-//
-//      "colorFromRect"_sigma(p_0, p_1)
-//          = int_{p_{0_y}}^{p_{1_y}} int_{p_{1_x}}^{p_{0_x}} G_sigma(y) G_sigma(x) dx dy
-//          = 1/4 ("erf"_sigma(p_{1_x}) - "erf"_sigma(p_{0_x}))
-//              ("erf"_sigma(p_{1_y}) - "erf"_sigma(p_{0_y}))
-float colorFromRect(vec2 p0, vec2 p1, float sigma) {
-    return (erfSigma(p1.x, sigma) - erfSigma(p0.x, sigma)) *
-        (erfSigma(p1.y, sigma) - erfSigma(p0.y, sigma)) / 4.0;
-}
-
-// Returns the `x` coordinate on the ellipse with the given radii for the given `y` coordinate:
-//
-//      "ellipsePoint"(y, y_0, a, b) = a sqrt(1 - ((y - y_0) / b)^2)
-float ellipsePoint(float y, float y0, vec2 radii) {
-    float bStep = (y - y0) / radii.y;
-    return radii.x * sqrt(1.0 - bStep * bStep);
-}
-
-// A helper function to compute the value that needs to be subtracted to accommodate the border
-// corners.
-//
-//     "colorCutout"_sigma(x_{0_l}, x_{0_r}, y_0, y_{min}, y_{max}, a, b)
-//          = int_{y_{min}}^{y_{max}}
-//              int_{x_{0_r} + "ellipsePoint"(y, y_0, a, b)}^{x_{0_r} + a} G_sigma(y) G_sigma(x) dx
-//              + int_{x_{0_l} - a}^{x_{0_l} - "ellipsePoint"(y, y_0, a, b)} G_sigma(y) G_sigma(x)
-//                  dx dy
-//          = int_{y_{min}}^{y_{max}} 1/2 G_sigma(y)
-//              ("erf"_sigma(x_{0_r} + a) - "erf"_sigma(x_{0_r} + "ellipsePoint"(y, y_0, a, b)) +
-//               "erf"_sigma(x_{0_l} - "ellipsePoint"(y, y_0, a, b)) - "erf"_sigma(x_{0_l} - a))
-//
-// with the outer integral evaluated numerically.
-float colorCutoutGeneral(float x0l,
-                         float x0r,
-                         float y0,
-                         float yMin,
-                         float yMax,
-                         vec2 radii,
-                         float sigma) {
-    float sum = 0.0;
-    for (float y = yMin; y <= yMax; y += 1.0) {
-        float xEllipsePoint = ellipsePoint(y, y0, radii);
-        sum += gauss(y, sigma) *
-            (erfSigma(x0r + radii.x, sigma) - erfSigma(x0r + xEllipsePoint, sigma) +
-             erfSigma(x0l - xEllipsePoint, sigma) - erfSigma(x0l - radii.x, sigma));
-    }
-    return sum / 2.0;
-}
-
-// The value that needs to be subtracted to accommodate the top border corners.
-float colorCutoutTop(float x0l, float x0r, float y0, vec2 radii, float sigma) {
-    return colorCutoutGeneral(x0l, x0r, y0, y0, y0 + radii.y, radii, sigma);
-}
-
-// The value that needs to be subtracted to accommodate the bottom border corners.
-float colorCutoutBottom(float x0l, float x0r, float y0, vec2 radii, float sigma) {
-    return colorCutoutGeneral(x0l, x0r, y0, y0 - radii.y, y0, radii, sigma);
-}
-
-// The blurred color value for the point at `pos` with the top left corner of the box at
-// `p_{0_"rect"}` and the bottom right corner of the box at `p_{1_"rect"}`.
-float color(vec2 pos, vec2 p0Rect, vec2 p1Rect, vec2 radii, float sigma) {
-    // Compute the vector distances `p_0` and `p_1`.
-    vec2 p0 = p0Rect - pos, p1 = p1Rect - pos;
-
-    // Compute the basic color `"colorFromRect"_sigma(p_0, p_1)`. This is all we have to do if
-    // the box is unrounded.
-    float cRect = colorFromRect(p0, p1, sigma);
-    if (radii.x == 0.0 || radii.y == 0.0)
-        return cRect;
-
-    // Compute the inner corners of the box, taking border radii into account: `x_{0_l}`,
-    // `y_{0_t}`, `x_{0_r}`, and `y_{0_b}`.
-    float x0l = p0.x + radii.x;
-    float y0t = p1.y - radii.y;
-    float x0r = p1.x - radii.x;
-    float y0b = p0.y + radii.y;
-
-    // Compute the final color:
-    //
-    //     "colorFromRect"_sigma(p_0, p_1) -
-    //          ("colorCutoutTop"_sigma(x_{0_l}, x_{0_r}, y_{0_t}, a, b) +
-    //           "colorCutoutBottom"_sigma(x_{0_l}, x_{0_r}, y_{0_b}, a, b))
-    float cCutoutTop = colorCutoutTop(x0l, x0r, y0t, radii, sigma);
-    float cCutoutBottom = colorCutoutBottom(x0l, x0r, y0b, radii, sigma);
-    return cRect - (cCutoutTop + cCutoutBottom);
-}
-
 void main(void) {
-    vec2 pos = vPos.xy;
-    vec2 p0Rect = vBoxShadowRect.xy, p1Rect = vBoxShadowRect.zw;
-    vec2 radii = vBorderRadii.xy;
-    float sigma = vBlurRadius / 2.0;
-    float value = color(pos, p0Rect, p1Rect, radii, sigma);
-
-    value = max(value, 0.0);
-    oFragColor = vColor * vec4(1.0, 1.0, 1.0, vInverted == 1.0 ? 1.0 - value : value);
+    vec2 uv = min(vec2(1.0), vMirrorPoint - abs(vUv.xy - vMirrorPoint));
+    uv = mix(vCacheUvRectCoords.xy, vCacheUvRectCoords.zw, uv);
+    oFragColor = vColor * texture(sCache, vec3(uv, vUv.z));
 }
diff --git a/resources/shaders/ps_box_shadow.glsl b/resources/shaders/ps_box_shadow.glsl
index 26fdba588f36..40faee87f583 100644
--- a/resources/shaders/ps_box_shadow.glsl
+++ b/resources/shaders/ps_box_shadow.glsl
@@ -2,10 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-varying vec2 vPos;
 flat varying vec4 vColor;
-flat varying vec2 vBorderRadii;
-flat varying float vBlurRadius;
-flat varying vec4 vBoxShadowRect;
-flat varying vec4 vSrcRect;
-flat varying float vInverted;
+
+varying vec3 vUv;
+flat varying vec2 vMirrorPoint;
+flat varying vec4 vCacheUvRectCoords;
diff --git a/resources/shaders/ps_box_shadow.vs.glsl b/resources/shaders/ps_box_shadow.vs.glsl
index e863ab0a8fc3..930aef9062e3 100644
--- a/resources/shaders/ps_box_shadow.vs.glsl
+++ b/resources/shaders/ps_box_shadow.vs.glsl
@@ -13,11 +13,19 @@ void main(void) {
                                  prim.layer,
                                  prim.tile);
 
-    vPos = vi.local_clamped_pos;
+    RenderTaskData child_task = fetch_render_task(prim.user_data.z);
+    vUv.z = child_task.data1.x;
+
+    // Constant offsets to inset from bilinear filtering border.
+    vec2 patch_origin = child_task.data0.xy + vec2(1.0);
+    vec2 patch_size_device_pixels = child_task.data0.zw - vec2(2.0);
+    vec2 patch_size = patch_size_device_pixels / uDevicePixelRatio;
+
+    vUv.xy = (vi.local_clamped_pos - prim.local_rect.xy) / patch_size;
+    vMirrorPoint = 0.5 * prim.local_rect.zw / patch_size;
+
+    vec2 texture_size = vec2(textureSize(sCache, 0));
+    vCacheUvRectCoords = vec4(patch_origin, patch_origin + patch_size_device_pixels) / texture_size.xyxy;
+
     vColor = bs.color;
-    vBorderRadii = bs.border_radii_blur_radius_inverted.xy;
-    vBlurRadius = bs.border_radii_blur_radius_inverted.z;
-    vBoxShadowRect = vec4(bs.bs_rect.xy, bs.bs_rect.xy + bs.bs_rect.zw);
-    vSrcRect = vec4(bs.src_rect.xy, bs.src_rect.xy + bs.src_rect.zw);
-    vInverted = bs.border_radii_blur_radius_inverted.w;
 }