diff --git a/gfx/thebes/GLContextProviderCGL.mm b/gfx/thebes/GLContextProviderCGL.mm
index e709215eb8e8..908a977fdc9c 100644
--- a/gfx/thebes/GLContextProviderCGL.mm
+++ b/gfx/thebes/GLContextProviderCGL.mm
@@ -278,6 +278,10 @@ GLContextCGL::ResizeOffscreen(const gfxIntSize& aNewSize)
             return false;
         }
 
+        if (!ResizeOffscreenFBO(aNewSize, false)) {
+            return false;
+        }
+
         [mPBuffer release];
         mPBuffer = pb;
 
@@ -293,7 +297,7 @@ GLContextCGL::ResizeOffscreen(const gfxIntSize& aNewSize)
         return true;
     }
 
-    return ResizeOffscreenFBO(aNewSize);
+    return ResizeOffscreenFBO(aNewSize, true);
 }
 
 class TextureImageCGL : public BasicTextureImage
@@ -532,8 +536,7 @@ CreateOffscreenPBufferContext(const gfxIntSize& aSize,
 }
 
 static already_AddRefed<GLContextCGL>
-CreateOffscreenFBOContext(const gfxIntSize& aSize,
-                          const ContextFormat& aFormat,
+CreateOffscreenFBOContext(const ContextFormat& aFormat,
                           bool aShare = true)
 {
     if (!sCGLLibrary.EnsureInitialized()) {
@@ -561,15 +564,19 @@ already_AddRefed<GLContext>
 GLContextProviderCGL::CreateOffscreen(const gfxIntSize& aSize,
                                       const ContextFormat& aFormat)
 {
+    ContextFormat actualFormat(aFormat);
+    actualFormat.samples = 0;
+
     nsRefPtr<GLContextCGL> glContext;
     
     NS_ENSURE_TRUE(Preferences::GetRootBranch(), nsnull);
     const bool preferFBOs = Preferences::GetBool("cgl.prefer-fbo", false);
     if (!preferFBOs)
     {
-        glContext = CreateOffscreenPBufferContext(aSize, aFormat);
+        glContext = CreateOffscreenPBufferContext(aSize, actualFormat);
         if (glContext &&
-            glContext->Init())
+            glContext->Init() &&
+            glContext->ResizeOffscreenFBO(aSize, false))
         {
             glContext->mOffscreenSize = aSize;
             glContext->mOffscreenActualSize = aSize;
@@ -581,10 +588,10 @@ GLContextProviderCGL::CreateOffscreen(const gfxIntSize& aSize,
     }
 
     // try a FBO as second choice
-    glContext = CreateOffscreenFBOContext(aSize, aFormat);
+    glContext = CreateOffscreenFBOContext(actualFormat);
     if (glContext &&
         glContext->Init() &&
-        glContext->ResizeOffscreenFBO(aSize))
+        glContext->ResizeOffscreenFBO(aSize, true))
     {
         return glContext.forget();
     }
@@ -613,8 +620,7 @@ GLContextProviderCGL::GetGlobalContext()
         // than 16x16 in size; also 16x16 is POT so that we can do
         // a FBO with it on older video cards.  A FBO context for
         // sharing is preferred since it has no associated target.
-        gGlobalContext = CreateOffscreenFBOContext(gfxIntSize(16, 16),
-                                                   ContextFormat(ContextFormat::BasicRGB24),
+        gGlobalContext = CreateOffscreenFBOContext(ContextFormat(ContextFormat::BasicRGB24),
                                                    false);
         if (!gGlobalContext || !static_cast<GLContextCGL*>(gGlobalContext.get())->Init()) {
             NS_WARNING("Couldn't init gGlobalContext.");