diff --git a/components/script/dom/webidls/XRSession.webidl b/components/script/dom/webidls/XRSession.webidl
index 7cf25bf8c367..a07fa355e6eb 100644
--- a/components/script/dom/webidls/XRSession.webidl
+++ b/components/script/dom/webidls/XRSession.webidl
@@ -17,7 +17,7 @@ interface XRSession : EventTarget {
   // // Attributes
   readonly attribute XRSessionMode mode;
   // readonly attribute XRPresentationContext outputContext;
-  // readonly attribute XREnvironmentBlendMode environmentBlendMode;
+  readonly attribute XREnvironmentBlendMode environmentBlendMode;
 
   attribute double depthNear;
   attribute double depthFar;
diff --git a/components/script/dom/xrsession.rs b/components/script/dom/xrsession.rs
index 93837255f37e..997d88b34bfe 100644
--- a/components/script/dom/xrsession.rs
+++ b/components/script/dom/xrsession.rs
@@ -5,6 +5,7 @@
 use crate::dom::bindings::codegen::Bindings::VRDisplayBinding::VRDisplayMethods;
 use crate::dom::bindings::codegen::Bindings::XRBinding::XRSessionMode;
 use crate::dom::bindings::codegen::Bindings::XRSessionBinding;
+use crate::dom::bindings::codegen::Bindings::XRSessionBinding::XREnvironmentBlendMode;
 use crate::dom::bindings::codegen::Bindings::XRSessionBinding::XRFrameRequestCallback;
 use crate::dom::bindings::codegen::Bindings::XRSessionBinding::XRSessionMethods;
 use crate::dom::bindings::codegen::Bindings::XRWebGLLayerBinding::XRWebGLLayerMethods;
@@ -26,6 +27,7 @@ pub struct XRSession {
     eventtarget: EventTarget,
     display: Dom<VRDisplay>,
     base_layer: MutNullableDom<XRLayer>,
+    blend_mode: XREnvironmentBlendMode,
 }
 
 impl XRSession {
@@ -34,6 +36,8 @@ impl XRSession {
             eventtarget: EventTarget::new_inherited(),
             display: Dom::from_ref(display),
             base_layer: Default::default(),
+            // we don't yet support any AR devices
+            blend_mode: XREnvironmentBlendMode::Opaque,
         }
     }
 
@@ -102,4 +106,9 @@ impl XRSessionMethods for XRSession {
     fn CancelAnimationFrame(&self, frame: i32) {
         self.display.xr_cancel_raf(frame)
     }
+
+    /// https://immersive-web.github.io/webxr/#dom-xrsession-environmentblendmode
+    fn EnvironmentBlendMode(&self) -> XREnvironmentBlendMode {
+        self.blend_mode
+    }
 }