diff --git a/gfx/layers/composite/ContainerLayerComposite.cpp b/gfx/layers/composite/ContainerLayerComposite.cpp
index 68c339de04a..9418f1bb80c 100644
--- a/gfx/layers/composite/ContainerLayerComposite.cpp
+++ b/gfx/layers/composite/ContainerLayerComposite.cpp
@@ -67,7 +67,7 @@ LayerHasCheckerboardingAPZC(Layer* aLayer, gfxRGBA* aOutColor)
 }
 
 /**
- * Returns a rectangle of content painted opaquely by aLayer. Very consertative;
+ * Returns a rectangle of content painted opaquely by aLayer. Very conservative;
  * bails by returning an empty rect in any tricky situations.
  */
 static nsIntRect
diff --git a/layout/base/FrameLayerBuilder.cpp b/layout/base/FrameLayerBuilder.cpp
index 2be83426883..3a8b26220c0 100644
--- a/layout/base/FrameLayerBuilder.cpp
+++ b/layout/base/FrameLayerBuilder.cpp
@@ -2324,6 +2324,27 @@ IsItemAreaInWindowOpaqueRegion(nsDisplayListBuilder* aBuilder,
   return aBuilder->GetWindowOpaqueRegion().Contains(aComponentAlphaBounds);
 }
 
+// Return true if aItem is a uniform color over the intersection of its
+// visible rect, bounds rect, and clip rect.
+static bool
+IsDisplayItemUniform(nsDisplayListBuilder* aBuilder,
+                     nsDisplayItem* aItem,
+                     const DisplayItemClip& aClip,
+                     nscolor* aUniformColor)
+{
+  bool uniform = aItem->IsUniform(aBuilder, aUniformColor);
+  if (!uniform) {
+    return false;
+  }
+  bool snap;
+  // Check to see if rounded-rect clipping affects the intersection of the
+  // item's visible and bounds rects. If it doesn't, then we're uniform over
+  // the intersection of those rects and the clip rect.
+  nsRect visibleRect =
+    aItem->GetBounds(aBuilder, &snap).Intersect(aItem->GetVisibleRect());
+  return !aClip.IsRectClippedByRoundedCorner(visibleRect);
+}
+
 void
 PaintedLayerData::Accumulate(ContainerState* aState,
                             nsDisplayItem* aItem,
@@ -2351,7 +2372,16 @@ PaintedLayerData::Accumulate(ContainerState* aState,
   bool clipMatches = mItemClip == aClip;
   mItemClip = aClip;
 
-  if (!mIsSolidColorInVisibleRegion && mOpaqueRegion.Contains(aDrawRect) &&
+  nscolor uniformColor;
+  // If a rounded corner affects the visible area of aItem (the intersection
+  // of its visible rect with its bounds), then it's not really uniform over
+  // its bounds. Implementations of nsDisplayItem::IsUniform do not
+  // consider this clipping.
+  bool isUniform = IsDisplayItemUniform(aState->mBuilder, aItem, aClip,
+                                        &uniformColor);
+
+  if (!mIsSolidColorInVisibleRegion && !isUniform &&
+      mOpaqueRegion.Contains(aDrawRect) &&
       mVisibleRegion.Contains(aVisibleRect) && !mImage) {
     // A very common case! Most pages have a PaintedLayer with the page
     // background (opaque) visible and most or all of the page content over the
@@ -2378,9 +2408,6 @@ PaintedLayerData::Accumulate(ContainerState* aState,
     mImage = nullptr;
   }
 
-  nscolor uniformColor;
-  bool isUniform = aItem->IsUniform(aState->mBuilder, &uniformColor);
-
   // Some display items have to exist (so they can set forceTransparentSurface
   // below) but don't draw anything. They'll return true for isUniform but
   // a color with opacity 0.
@@ -2395,12 +2422,16 @@ PaintedLayerData::Accumulate(ContainerState* aState,
         isUniform = false;
         FLB_LOG_PAINTED_LAYER_DECISION(this, "  Display item does not cover the visible rect\n");
       }
-    }
-    if (isUniform) {
+
       if (mVisibleRegion.IsEmpty()) {
         // This color is all we have
         mSolidColor = uniformColor;
         mIsSolidColorInVisibleRegion = true;
+      } else if (NS_GET_A(uniformColor) == 255 &&
+                 aVisibleRect.Contains(mVisibleRegion.GetBounds())) {
+        // This color covers everything else in the layer
+        mSolidColor = uniformColor;
+        mIsSolidColorInVisibleRegion = true;
       } else if (mIsSolidColorInVisibleRegion &&
                  mVisibleRegion.IsEqual(nsIntRegion(aVisibleRect)) &&
                  clipMatches) {