Bug 366128. Restrict disabling of floats in XUL to cases where the container is not a float containing block. r+sr=bzbarsky

layout/base/nsCSSFrameConstructor.cpp

@@ -5792,6 +5792,8 @@ nsCSSFrameConstructor::ConstructXULFrame(nsFrameConstructorState& aState,
                aTag == nsGkAtoms::description) {
         if ((aTag == nsGkAtoms::label || aTag == nsGkAtoms::description) && 
             (! aContent->HasAttr(kNameSpaceID_None, nsGkAtoms::value))) {
+          // XXX we should probably be calling ConstructBlock here to handle
+          // things like columns etc
           newFrame = NS_NewAreaFrame(mPresShell, aStyleContext,
                                      NS_BLOCK_SPACE_MGR | NS_BLOCK_MARGIN_ROOT);
         }
@@ -6114,12 +6116,14 @@ nsCSSFrameConstructor::ConstructXULFrame(nsFrameConstructorState& aState,
     }
 #endif
 
-    // Push a null float containing block to disable floating within xul
+    // If the new frame isn't a float containing block, then push a null
+    // float containing block to disable floats. This is needed to disable
+    // floats within XUL frames.
     nsFrameConstructorSaveState floatSaveState;
-    if (newFrame->IsBoxFrame()) {
-      aState.PushFloatContainingBlock(nsnull, floatSaveState, PR_FALSE,
-                                      PR_FALSE);
-    }
+    PRBool isFloatContainingBlock =
+      newFrame->GetContentInsertionFrame()->IsFloatContainingBlock();
+    aState.PushFloatContainingBlock(isFloatContainingBlock ? newFrame : nsnull,
+                                    floatSaveState, PR_FALSE, PR_FALSE);
 
     // Process the child content if requested
     nsFrameItems childItems;