diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index 24d112b92ce..8ac43391e86 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -66,7 +66,6 @@ enum UnableToComposite {
 
 #[derive(Debug, PartialEq)]
 enum NotReadyToPaint {
-    AnimationsActive,
     JustNotifiedConstellation,
     WaitingOnConstellation,
 }
@@ -234,10 +233,6 @@ pub(crate) struct PipelineDetails {
 }
 
 impl PipelineDetails {
-    pub(crate) fn animations_or_animation_callbacks_running(&self) -> bool {
-        self.animations_running || self.animation_callbacks_running
-    }
-
     pub(crate) fn animation_callbacks_running(&self) -> bool {
         self.animation_callbacks_running
     }
@@ -1273,13 +1268,6 @@ impl IOCompositor {
             .get(&pipeline_id)
     }
 
-    // Check if any pipelines currently have active animations or animation callbacks.
-    fn animations_or_animation_callbacks_running(&self) -> bool {
-        self.webview_renderers
-            .iter()
-            .any(WebViewRenderer::animations_or_animation_callbacks_running)
-    }
-
     /// Returns true if any animation callbacks (ie `requestAnimationFrame`) are waiting for a response.
     fn animation_callbacks_running(&self) -> bool {
         self.webview_renderers
@@ -1424,13 +1412,6 @@ impl IOCompositor {
         }
 
         if opts::get().wait_for_stable_image {
-            // The current image may be ready to output. However, if there are animations active,
-            // continue waiting for the image output to be stable AND all active animations to complete.
-            if self.animations_or_animation_callbacks_running() {
-                return Err(UnableToComposite::NotReadyToPaintImage(
-                    NotReadyToPaint::AnimationsActive,
-                ));
-            }
             if let Err(result) = self.is_ready_to_paint_image_output() {
                 return Err(UnableToComposite::NotReadyToPaintImage(result));
             }
diff --git a/components/compositing/webview_renderer.rs b/components/compositing/webview_renderer.rs
index 917d909a7fd..6e216582f3b 100644
--- a/components/compositing/webview_renderer.rs
+++ b/components/compositing/webview_renderer.rs
@@ -139,12 +139,6 @@ impl WebViewRenderer {
         }
     }
 
-    pub(crate) fn animations_or_animation_callbacks_running(&self) -> bool {
-        self.pipelines
-            .values()
-            .any(PipelineDetails::animations_or_animation_callbacks_running)
-    }
-
     pub(crate) fn animation_callbacks_running(&self) -> bool {
         self.pipelines
             .values()
diff --git a/tests/wpt/meta/css/css-animations/animation-delay-008.html.ini b/tests/wpt/meta/css/css-animations/animation-delay-008.html.ini
index 9daaa6465b7..dae9a4fc7aa 100644
--- a/tests/wpt/meta/css/css-animations/animation-delay-008.html.ini
+++ b/tests/wpt/meta/css/css-animations/animation-delay-008.html.ini
@@ -1,2 +1,2 @@
 [animation-delay-008.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-animations/animation-delay-009.html.ini b/tests/wpt/meta/css/css-animations/animation-delay-009.html.ini
index 6b52057e84c..c889c72e9dc 100644
--- a/tests/wpt/meta/css/css-animations/animation-delay-009.html.ini
+++ b/tests/wpt/meta/css/css-animations/animation-delay-009.html.ini
@@ -1,2 +1,2 @@
 [animation-delay-009.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-animations/animation-important-002.html.ini b/tests/wpt/meta/css/css-animations/animation-important-002.html.ini
index 3f47d2b7f71..3e0c74fae76 100644
--- a/tests/wpt/meta/css/css-animations/animation-important-002.html.ini
+++ b/tests/wpt/meta/css/css-animations/animation-important-002.html.ini
@@ -1,2 +1,2 @@
 [animation-important-002.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-animations/crashtests/chrome-bug-404743651.html.ini b/tests/wpt/meta/css/css-animations/crashtests/chrome-bug-404743651.html.ini
deleted file mode 100644
index d99d36b7a59..00000000000
--- a/tests/wpt/meta/css/css-animations/crashtests/chrome-bug-404743651.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[chrome-bug-404743651.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-animations/inheritance-pseudo-element.html.ini b/tests/wpt/meta/css/css-animations/inheritance-pseudo-element.html.ini
index c0471d39fa9..8fe05e127ad 100644
--- a/tests/wpt/meta/css/css-animations/inheritance-pseudo-element.html.ini
+++ b/tests/wpt/meta/css/css-animations/inheritance-pseudo-element.html.ini
@@ -1,2 +1,2 @@
 [inheritance-pseudo-element.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-animations/transform-animation-under-large-scale.html.ini b/tests/wpt/meta/css/css-animations/transform-animation-under-large-scale.html.ini
deleted file mode 100644
index f97ef08100d..00000000000
--- a/tests/wpt/meta/css/css-animations/transform-animation-under-large-scale.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[transform-animation-under-large-scale.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-animations/translation-animation-on-important-property.html.ini b/tests/wpt/meta/css/css-animations/translation-animation-on-important-property.html.ini
deleted file mode 100644
index adaffb97380..00000000000
--- a/tests/wpt/meta/css/css-animations/translation-animation-on-important-property.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[translation-animation-on-important-property.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-animations/translation-animation-subpixel-offset.html.ini b/tests/wpt/meta/css/css-animations/translation-animation-subpixel-offset.html.ini
deleted file mode 100644
index baebc61857a..00000000000
--- a/tests/wpt/meta/css/css-animations/translation-animation-subpixel-offset.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[translation-animation-subpixel-offset.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-element-not-visible-at-current-viewport.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-element-not-visible-at-current-viewport.html.ini
deleted file mode 100644
index ef5b08cbb56..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-element-not-visible-at-current-viewport.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-element-not-visible-at-current-viewport.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-fragmented.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-fragmented.html.ini
deleted file mode 100644
index 08925dcbe3c..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-fragmented.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-fragmented.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-in-body.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-in-body.html.ini
deleted file mode 100644
index 7bb772573a2..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-in-body.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-in-body.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-non-zero-size-element-change-to-zero.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-non-zero-size-element-change-to-zero.html.ini
deleted file mode 100644
index 7a4839a8e6f..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-non-zero-size-element-change-to-zero.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-non-zero-size-element-change-to-zero.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-images.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-images.html.ini
deleted file mode 100644
index 7e66313f326..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-images.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-with-images.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-table2.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-table2.html.ini
deleted file mode 100644
index 99990bcea55..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-table2.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-with-table2.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-table3.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-table3.html.ini
deleted file mode 100644
index 99394fb1525..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-with-table3.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-with-table3.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-zero-size-element-change-to-non-zero.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-zero-size-element-change-to-non-zero.html.ini
deleted file mode 100644
index ba57feda819..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-animation-zero-size-element-change-to-non-zero.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-zero-size-element-change-to-non-zero.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-transition.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-transition.html.ini
deleted file mode 100644
index 866c19a78f8..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-transition.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-transition.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/background-color-transparent-animation-in-body.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/background-color-transparent-animation-in-body.html.ini
deleted file mode 100644
index eb56611f9f7..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/background-color-transparent-animation-in-body.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-transparent-animation-in-body.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-backgrounds/animations/invalidation/background-color-animation-with-zero-alpha.html.ini b/tests/wpt/meta/css/css-backgrounds/animations/invalidation/background-color-animation-with-zero-alpha.html.ini
deleted file mode 100644
index 38cc83c5f52..00000000000
--- a/tests/wpt/meta/css/css-backgrounds/animations/invalidation/background-color-animation-with-zero-alpha.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[background-color-animation-with-zero-alpha.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-cascade/important-prop.html.ini b/tests/wpt/meta/css/css-cascade/important-prop.html.ini
deleted file mode 100644
index f251ce6a140..00000000000
--- a/tests/wpt/meta/css/css-cascade/important-prop.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[important-prop.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-conditional/container-queries/crashtests/size-change-during-transition-crash.html.ini b/tests/wpt/meta/css/css-conditional/container-queries/crashtests/size-change-during-transition-crash.html.ini
deleted file mode 100644
index d4f04e8e769..00000000000
--- a/tests/wpt/meta/css/css-conditional/container-queries/crashtests/size-change-during-transition-crash.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[size-change-during-transition-crash.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-fonts/font-size-monospace-adjust.html.ini b/tests/wpt/meta/css/css-fonts/font-size-monospace-adjust.html.ini
deleted file mode 100644
index 700d382f080..00000000000
--- a/tests/wpt/meta/css/css-fonts/font-size-monospace-adjust.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[font-size-monospace-adjust.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-pseudo/first-line-inherited-with-transition.html.ini b/tests/wpt/meta/css/css-pseudo/first-line-inherited-with-transition.html.ini
index ea74d2e64ef..f35bb427091 100644
--- a/tests/wpt/meta/css/css-pseudo/first-line-inherited-with-transition.html.ini
+++ b/tests/wpt/meta/css/css-pseudo/first-line-inherited-with-transition.html.ini
@@ -1,2 +1,2 @@
 [first-line-inherited-with-transition.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-shadow-parts/animation-part.html.ini b/tests/wpt/meta/css/css-shadow-parts/animation-part.html.ini
deleted file mode 100644
index 7d3d4520485..00000000000
--- a/tests/wpt/meta/css/css-shadow-parts/animation-part.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[animation-part.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-transforms/animation/rotate-animation-with-will-change-transform-001.html.ini b/tests/wpt/meta/css/css-transforms/animation/rotate-animation-with-will-change-transform-001.html.ini
deleted file mode 100644
index 70854f42421..00000000000
--- a/tests/wpt/meta/css/css-transforms/animation/rotate-animation-with-will-change-transform-001.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[rotate-animation-with-will-change-transform-001.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-transforms/backface-visibility-hidden-animated-001.html.ini b/tests/wpt/meta/css/css-transforms/backface-visibility-hidden-animated-001.html.ini
deleted file mode 100644
index 18825dc532c..00000000000
--- a/tests/wpt/meta/css/css-transforms/backface-visibility-hidden-animated-001.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[backface-visibility-hidden-animated-001.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-transforms/backface-visibility-hidden-animated-002.html.ini b/tests/wpt/meta/css/css-transforms/backface-visibility-hidden-animated-002.html.ini
deleted file mode 100644
index 90198176f4d..00000000000
--- a/tests/wpt/meta/css/css-transforms/backface-visibility-hidden-animated-002.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[backface-visibility-hidden-animated-002.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-combine.html.ini b/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-combine.html.ini
index d026f369754..13fb4379bc3 100644
--- a/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-combine.html.ini
+++ b/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-combine.html.ini
@@ -1,2 +1,2 @@
 [individual-transform-combine.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-ordering.html.ini b/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-ordering.html.ini
index 1dc33a5f66e..0640a5c3f0b 100644
--- a/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-ordering.html.ini
+++ b/tests/wpt/meta/css/css-transforms/individual-transform/animation/individual-transform-ordering.html.ini
@@ -1,2 +1,2 @@
 [individual-transform-ordering.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-transforms/individual-transform/stacking-context-001.html.ini b/tests/wpt/meta/css/css-transforms/individual-transform/stacking-context-001.html.ini
index f5e21fbaa39..ab91d7dbff3 100644
--- a/tests/wpt/meta/css/css-transforms/individual-transform/stacking-context-001.html.ini
+++ b/tests/wpt/meta/css/css-transforms/individual-transform/stacking-context-001.html.ini
@@ -1,2 +1,2 @@
 [stacking-context-001.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-transitions/allow-discrete-auto-inset.html.ini b/tests/wpt/meta/css/css-transitions/allow-discrete-auto-inset.html.ini
deleted file mode 100644
index 361bdd35c68..00000000000
--- a/tests/wpt/meta/css/css-transitions/allow-discrete-auto-inset.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[allow-discrete-auto-inset.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-values/vh-interpolate-pct.html.ini b/tests/wpt/meta/css/css-values/vh-interpolate-pct.html.ini
deleted file mode 100644
index be2538e602f..00000000000
--- a/tests/wpt/meta/css/css-values/vh-interpolate-pct.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[vh-interpolate-pct.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-values/vh-interpolate-px.html.ini b/tests/wpt/meta/css/css-values/vh-interpolate-px.html.ini
deleted file mode 100644
index bf182b798a0..00000000000
--- a/tests/wpt/meta/css/css-values/vh-interpolate-px.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[vh-interpolate-px.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/css-values/vh-interpolate-vh.html.ini b/tests/wpt/meta/css/css-values/vh-interpolate-vh.html.ini
deleted file mode 100644
index 7fd394999f3..00000000000
--- a/tests/wpt/meta/css/css-values/vh-interpolate-vh.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[vh-interpolate-vh.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/css/filter-effects/crashtests/broken-reference-crash-001.html.ini b/tests/wpt/meta/css/filter-effects/crashtests/broken-reference-crash-001.html.ini
deleted file mode 100644
index 28668363c2d..00000000000
--- a/tests/wpt/meta/css/filter-effects/crashtests/broken-reference-crash-001.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[broken-reference-crash-001.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-animation-001.html.ini b/tests/wpt/meta/html/rendering/widgets/appearance/appearance-animation-001.html.ini
deleted file mode 100644
index a15e196e8fc..00000000000
--- a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-animation-001.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[appearance-animation-001.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-animation-002.html.ini b/tests/wpt/meta/html/rendering/widgets/appearance/appearance-animation-002.html.ini
index fb11e60c0eb..d0d879ae4a2 100644
--- a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-animation-002.html.ini
+++ b/tests/wpt/meta/html/rendering/widgets/appearance/appearance-animation-002.html.ini
@@ -1,2 +1,2 @@
 [appearance-animation-002.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-001.html.ini b/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-001.html.ini
deleted file mode 100644
index 4d7f16342fb..00000000000
--- a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-001.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[appearance-transition-001.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-002.html.ini b/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-002.html.ini
deleted file mode 100644
index a5468b7465a..00000000000
--- a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-002.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[appearance-transition-002.html]
-  expected: TIMEOUT
diff --git a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-003.html.ini b/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-003.html.ini
index 784ec6e4053..e6c40338141 100644
--- a/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-003.html.ini
+++ b/tests/wpt/meta/html/rendering/widgets/appearance/appearance-transition-003.html.ini
@@ -1,2 +1,2 @@
 [appearance-transition-003.html]
-  expected: TIMEOUT
+  expected: FAIL
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 63d4f0ed542..4599cc850b4 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -2887,7 +2887,7 @@
      ]
     ],
     "incremental_trailing_whitespace_a.html": [
-     "f59bd91d9ea23effec2a888649e345937cf0addd",
+     "eca05c4f79fb786492e81aa7881aaa0d75899811",
      [
       null,
       [
@@ -3186,7 +3186,7 @@
      ]
     ],
     "inline_block_opacity_change.html": [
-     "aa51ab444cddb381b6ca76615a30573f49f6f6c3",
+     "6df5d7466d6569a7d1969d5c49a83a7a3564ef7b",
      [
       null,
       [
diff --git a/tests/wpt/mozilla/tests/css/incremental_trailing_whitespace_a.html b/tests/wpt/mozilla/tests/css/incremental_trailing_whitespace_a.html
index f59bd91d9ea..eca05c4f79f 100644
--- a/tests/wpt/mozilla/tests/css/incremental_trailing_whitespace_a.html
+++ b/tests/wpt/mozilla/tests/css/incremental_trailing_whitespace_a.html
@@ -1,5 +1,5 @@
 <!doctype html>
-<html>
+<html class="reftest-wait">
   <head>
     <meta charset="utf-8">
     <title>incremental trailing whitespace test</title>
@@ -19,9 +19,13 @@
       <div id="a" style="transition: all .1s ease-out;">Hello</div>
     </div>
     <script>
+      let transitioningDiv = document.querySelector('#a');
+      transitioningDiv.addEventListener('transitionend', () => {
+        document.documentElement.classList.remove("reftest-wait");
+      });
+
       document.body.offsetWidth; // force layout
-      document.querySelector('#a').classList.add('go');
-      // FIXME (#10245): Wait for the "transitionend" event.
+      transitioningDiv.classList.add('go');
     </script>
   </body>
 </html>
diff --git a/tests/wpt/mozilla/tests/css/inline_block_opacity_change.html b/tests/wpt/mozilla/tests/css/inline_block_opacity_change.html
index aa51ab444cd..6df5d7466d6 100644
--- a/tests/wpt/mozilla/tests/css/inline_block_opacity_change.html
+++ b/tests/wpt/mozilla/tests/css/inline_block_opacity_change.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<html>
+<html class="reftest-wait">
 <head>
     <link rel="match" href="inline_block_opacity_change_ref.html">
     <style>
@@ -19,8 +19,13 @@
 <body>
     <span style="transition: opacity .1s ease-out;" id="a">a</span>
     <script>
+            let transitioningSpan = document.querySelector('#a');
+            transitioningSpan.addEventListener("transitionend", () => {
+              document.documentElement.classList.remove("reftest-wait");
+            });
+
             document.body.offsetWidth; // force layout
-            document.querySelector('#a').classList.add('go');
+            transitioningSpan.classList.add('go');
     </script>
 </body>
 </html>