diff --git a/dom/nodes/moveBefore/tentative/continue-css-animation-left.html b/dom/nodes/moveBefore/tentative/continue-css-animation-left.html
new file mode 100644
index 00000000000000..8c7f73e3c933ce
--- /dev/null
+++ b/dom/nodes/moveBefore/tentative/continue-css-animation-left.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<title>Node.moveBefore should preserve CSS animation state (left)</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <section id="old-parent">
+    <div id="item"></div>
+  </section>
+  <section id="new-parent">
+  </section>
+  <style>
+    @keyframes anim {
+      from {
+        left: 100px;
+      }
+
+      to {
+        left: 400px;
+      }
+    }
+
+    section {
+      position: absolute;
+    }
+
+    #item {
+      position: relative;
+      width: 100px;
+      height: 100px;
+      background: green;
+      animation: 1s linear infinite alternate anim;
+      animation-delay: 100ms;
+    }
+  </style>
+  <script>
+    promise_test(async t => {
+      const item = document.querySelector("#item");
+      let num_events = 0;
+      await new Promise(resolve => addEventListener("animationstart", () => {
+        num_events++;
+        resolve();
+      }));
+
+      // Reparent item
+      document.body.querySelector("#new-parent").moveBefore(item, null);
+      await new Promise(resolve => requestAnimationFrame(() => resolve()));
+      assert_equals(num_events, 1);
+      assert_not_equals(getComputedStyle(item).left, "0px");
+    });
+  </script>
+</body>
diff --git a/dom/nodes/moveBefore/tentative/continue-css-animation-transform.html b/dom/nodes/moveBefore/tentative/continue-css-animation-transform.html
new file mode 100644
index 00000000000000..e7a285893aa0e4
--- /dev/null
+++ b/dom/nodes/moveBefore/tentative/continue-css-animation-transform.html
@@ -0,0 +1,48 @@
+<!DOCTYPE html>
+<title>Node.moveBefore should preserve CSS animation state (transform)</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+  <section id="old-parent">
+    <div id="item"></div>
+  </section>
+  <section id="new-parent">
+  </section>
+  <style>
+    @keyframes anim {
+      from {
+        transform: translateX(100px);
+      }
+
+      to {
+        transform: translateX(400px);
+      }
+    }
+
+    #item {
+      position: relative;
+      width: 100px;
+      height: 100px;
+      background: green;
+      animation: 1s linear infinite alternate anim;
+      animation-delay: 100ms;
+    }
+  </style>
+  <script>
+    promise_test(async t => {
+      const item = document.querySelector("#item");
+      let num_events = 0;
+      await new Promise(resolve => addEventListener("animationstart", () => {
+        num_events++;
+        resolve();
+      }));
+
+      // Reparent item
+      document.body.querySelector("#new-parent").moveBefore(item, null);
+      await new Promise(resolve => requestAnimationFrame(() => resolve()));
+      assert_equals(num_events, 1);
+      assert_not_equals(getComputedStyle(item).transform, "none");
+    });
+  </script>
+</body>
diff --git a/dom/nodes/moveBefore/tentative/continue-css-transition-left.html b/dom/nodes/moveBefore/tentative/continue-css-transition-left.html
new file mode 100644
index 00000000000000..2b8e04b26e469b
--- /dev/null
+++ b/dom/nodes/moveBefore/tentative/continue-css-transition-left.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<title>Node.moveBefore should preserve CSS transition state (left)</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+  <section id="old-parent">
+    <div id="item"></div>
+  </section>
+  <section id="new-parent">
+  </section>
+  <style>
+    #item {
+      width: 100px;
+      height: 100px;
+      background: green;
+      transition: left 10s;
+      position: absolute;
+      left: 0;
+    }
+
+    section {
+      position: relative;
+    }
+
+    body {
+      margin-left: 0;
+    }
+  </style>
+  <script>
+    promise_test(async t => {
+      const item = document.querySelector("#item");
+      assert_equals(item.getBoundingClientRect().x, 0);
+      item.style.left = "400px";
+      await new Promise(resolve => item.addEventListener("transitionstart", resolve));
+      document.querySelector("#new-parent").moveBefore(item, null);
+      await new Promise(resolve => requestAnimationFrame(() => resolve()));
+      assert_less_than(item.getBoundingClientRect().x, 399);
+    });
+  </script>
+</body>
diff --git a/dom/nodes/moveBefore/tentative/continue-css-transition-transform.html b/dom/nodes/moveBefore/tentative/continue-css-transition-transform.html
new file mode 100644
index 00000000000000..f09edca1449789
--- /dev/null
+++ b/dom/nodes/moveBefore/tentative/continue-css-transition-transform.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<title>Node.moveBefore should preserve CSS transition state (transform)</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+  <section id="old-parent">
+    <div id="item"></div>
+  </section>
+  <section id="new-parent">
+  </section>
+  <style>
+    #item {
+      width: 100px;
+      height: 100px;
+      background: green;
+      transition: transform 60s steps(1, jump-both);
+    }
+
+    body {
+      margin-left: 0;
+    }
+  </style>
+  <script>
+    promise_test(async t => {
+      const item = document.querySelector("#item");
+      assert_equals(item.getBoundingClientRect().x, 0);
+      item.style.transform = "translateX(400px)";
+      await new Promise(resolve => item.addEventListener("transitionstart", resolve));
+      document.querySelector("#new-parent").moveBefore(item, null);
+      await new Promise(resolve => requestAnimationFrame(() => resolve()));
+      assert_equals(item.getBoundingClientRect().x, 200);
+      assert_equals(item.getAnimations().length, 1);
+    });
+  </script>
+</body>
diff --git a/dom/nodes/moveBefore/tentative/css-animation-commit-styles.html b/dom/nodes/moveBefore/tentative/css-animation-commit-styles.html
new file mode 100644
index 00000000000000..86bb7c33e4261e
--- /dev/null
+++ b/dom/nodes/moveBefore/tentative/css-animation-commit-styles.html
@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<title>Calling commitStyles after Node.moveBefore should commit mid-transition value</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+  <section id="old-parent">
+    <div id="item"></div>
+  </section>
+  <section id="new-parent">
+  </section>
+  <style>
+    @keyframes anim {
+      from {
+        transform: translateX(100px);
+      }
+
+      to {
+        transform: translateX(400px);
+      }
+    }
+
+    #item {
+      position: relative;
+      width: 100px;
+      height: 100px;
+      background: green;
+      animation: 1s linear infinite alternate anim;
+      animation-delay: 100ms;
+    }
+  </style>
+  <script>
+    promise_test(async t => {
+      const item = document.querySelector("#item");
+      await new Promise(resolve => item.addEventListener("animationstart", resolve));
+
+      // Reparent item
+      document.body.querySelector("#new-parent").moveBefore(item, null);
+
+      item.getAnimations()[0].commitStyles();
+      assert_true("transform" in item.style);
+      assert_not_equals(item.style.transform, "none");
+    });
+  </script>
+</body>
diff --git a/dom/nodes/moveBefore/tentative/css-transition-trigger.html b/dom/nodes/moveBefore/tentative/css-transition-trigger.html
new file mode 100644
index 00000000000000..0cb5608a695e00
--- /dev/null
+++ b/dom/nodes/moveBefore/tentative/css-transition-trigger.html
@@ -0,0 +1,43 @@
+<!DOCTYPE html>
+<title>Node.moveBefore should trigger CSS transition state (left) if needed</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+  <section id="old-parent">
+    <div id="item"></div>
+  </section>
+  <section id="new-parent">
+  </section>
+  <style>
+    #item {
+      width: 100px;
+      height: 100px;
+      background: green;
+      transition: left 10s steps(1, jump-both);
+      position: absolute;
+      left: 0;
+    }
+
+    #new-parent #item {
+      left: 400px;
+    }
+
+    section {
+      position: relative;
+    }
+
+    body {
+      margin-left: 0;
+    }
+  </style>
+  <script>
+    promise_test(async t => {
+      const item = document.querySelector("#item");
+      assert_equals(item.getBoundingClientRect().x, 0);
+      document.querySelector("#new-parent").moveBefore(item, null);
+      await new Promise(resolve => item.addEventListener("transitionstart", resolve));
+      assert_equals(item.getBoundingClientRect().x, 200);
+    });
+  </script>
+</body>
