4 files changed, 33 insertions, 6 deletions
diff --git a/gfx/layers/client/ContentClient.cpp b/gfx/layers/client/ContentClient.cpp
index 3373230a9..50e159a23 100644
--- a/gfx/layers/client/ContentClient.cpp
+++ b/gfx/layers/client/ContentClient.cpp
@@ -78,8 +78,21 @@ ContentClient::CreateContentClient(CompositableForwarder* aForwarder)
   // We can't use double buffering when using image content with
   // Xrender support on Linux, as ContentHostDoubleBuffered is not
   // suited for direct uploads to the server.
+  // FIXME: Even though the comment above suggests that double buffering
+  //        is supposed to be disabled when Xrender support is being enabled
+  //        (and used), it really wasn't. Historically,
+  //        UseImageOffscreenSurfaces() was always false in GTK2 builds, thus
+  //        triggering the check, regardless of UseXRender().
+  //        Some time later, offscreen surfaces were always enabled, but the
+  //        Xrender functionality broke due to not using Xlib-based surfaces.
+  //        Using Xlib-based surfaces compatible with Xrender operations seems
+  //        to lead to weird graphical artifacts (bars and stripes) on some
+  //        hardware (Intel-based?) when displaying quickly-changing content,
+  //        so contrary to the statement above we'd better enable double
+  //        buffering - which also seems to not have any negative performance
+  //        impact.
   if (!gfxPlatformGtk::GetPlatform()->UseImageOffscreenSurfaces() ||
-      !gfxVars::UseXRender())
+       gfxVars::UseXRender())
 #endif
   {
     useDoubleBuffering = (LayerManagerComposite::SupportsDirectTexturing() &&
diff --git a/gfx/layers/composite/CanvasLayerComposite.cpp b/gfx/layers/composite/CanvasLayerComposite.cpp
index 3c8299e05..86f25b1ee 100644
--- a/gfx/layers/composite/CanvasLayerComposite.cpp
+++ b/gfx/layers/composite/CanvasLayerComposite.cpp
@@ -43,9 +43,13 @@ bool
 CanvasLayerComposite::SetCompositableHost(CompositableHost* aHost)
 {
   switch (aHost->GetType()) {
-    case CompositableType::IMAGE:
+    case CompositableType::IMAGE: {
+      if (mCompositableHost && aHost != mCompositableHost) {
+        mCompositableHost->Detach(this);
+      }
       mCompositableHost = aHost;
       return true;
+    }
     default:
       return false;
   }
diff --git a/gfx/layers/composite/ImageLayerComposite.cpp b/gfx/layers/composite/ImageLayerComposite.cpp
index bac9f3790..6867aaa22 100644
--- a/gfx/layers/composite/ImageLayerComposite.cpp
+++ b/gfx/layers/composite/ImageLayerComposite.cpp
@@ -50,9 +50,14 @@ bool
 ImageLayerComposite::SetCompositableHost(CompositableHost* aHost)
 {
   switch (aHost->GetType()) {
-    case CompositableType::IMAGE:
-      mImageHost = static_cast<ImageHost*>(aHost);
+    case CompositableType::IMAGE: {
+      ImageHost* newImageHost = static_cast<ImageHost*>(aHost);
+      if (mImageHost && newImageHost != mImageHost) {
+        mImageHost->Detach(this);
+      }
+      mImageHost = newImageHost;
       return true;
+    }
     default:
       return false;
   }
diff --git a/gfx/layers/composite/PaintedLayerComposite.cpp b/gfx/layers/composite/PaintedLayerComposite.cpp
index b58f5d690..232cc4ef4 100644
--- a/gfx/layers/composite/PaintedLayerComposite.cpp
+++ b/gfx/layers/composite/PaintedLayerComposite.cpp
@@ -49,9 +49,14 @@ PaintedLayerComposite::SetCompositableHost(CompositableHost* aHost)
   switch (aHost->GetType()) {
     case CompositableType::CONTENT_TILED:
     case CompositableType::CONTENT_SINGLE:
-    case CompositableType::CONTENT_DOUBLE:
-      mBuffer = static_cast<ContentHost*>(aHost);
+    case CompositableType::CONTENT_DOUBLE: {
+      ContentHost* newBuffer = static_cast<ContentHost*>(aHost);
+      if (mBuffer && newBuffer != mBuffer) {
+        mBuffer->Detach(this);
+      }
+      mBuffer = newBuffer;
       return true;
+    }
     default:
       return false;
   }