diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index 22ef7dae4270..87e1f2a5ea55 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -5061,8 +5061,8 @@ nsCSSFrameConstructor::FlushAccumulatedBlock(nsFrameConstructorState& aState,
   // MathML frame so that Get(Absolute/Float)ContainingBlockFor know that this
   // is not a suitable block.
   nsContainerFrame* blockFrame =
-      NS_NewMathMLmathBlockFrame(mPresShell, blockContext,
-                                 NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+    NS_NewMathMLmathBlockFrame(mPresShell, blockContext);
+  blockFrame->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
 
   InitAndRestoreFrame(aState, aContent, aParentFrame, blockFrame);
   ReparentFrames(this, blockFrame, aBlockItems);
@@ -5102,7 +5102,7 @@ nsCSSFrameConstructor::FindMathMLData(Element* aElement,
       static const FrameConstructionData sBlockMathData =
         FCDATA_DECL(FCDATA_FORCE_NULL_ABSPOS_CONTAINER |
                     FCDATA_WRAP_KIDS_IN_BLOCKS,
-                    NS_CreateNewMathMLmathBlockFrame);
+                    NS_NewMathMLmathBlockFrame);
       return &sBlockMathData;
     }
 
diff --git a/layout/forms/nsSelectsAreaFrame.cpp b/layout/forms/nsSelectsAreaFrame.cpp
index cb30e430f317..dd613ae9fd2b 100644
--- a/layout/forms/nsSelectsAreaFrame.cpp
+++ b/layout/forms/nsSelectsAreaFrame.cpp
@@ -17,7 +17,7 @@ NS_NewSelectsAreaFrame(nsIPresShell* aShell, nsStyleContext* aContext, nsFrameSt
 
   // We need NS_BLOCK_FLOAT_MGR to ensure that the options inside the select
   // aren't expanded by right floats outside the select.
-  it->SetFlags(aFlags | NS_BLOCK_FLOAT_MGR);
+  it->AddStateBits(aFlags | NS_BLOCK_FLOAT_MGR);
 
   return it;
 }
diff --git a/layout/generic/nsBlockFrame.cpp b/layout/generic/nsBlockFrame.cpp
index 912ddfb71511..cdf4ae78722e 100644
--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -6799,8 +6799,9 @@ nsBlockFrame::Init(nsIContent*       aContent,
 {
   if (aPrevInFlow) {
     // Copy over the inherited block frame bits from the prev-in-flow.
-    SetFlags(aPrevInFlow->GetStateBits() &
-             (NS_BLOCK_FLAGS_MASK & ~NS_BLOCK_FLAGS_NON_INHERITED_MASK));
+    RemoveStateBits(NS_BLOCK_FLAGS_MASK);
+    AddStateBits(aPrevInFlow->GetStateBits() &
+                 (NS_BLOCK_FLAGS_MASK & ~NS_BLOCK_FLAGS_NON_INHERITED_MASK));
   }
 
   nsContainerFrame::Init(aContent, aParent, aPrevInFlow);
diff --git a/layout/generic/nsBlockFrame.h b/layout/generic/nsBlockFrame.h
index 6adcecb98d6c..6f7ccb47023f 100644
--- a/layout/generic/nsBlockFrame.h
+++ b/layout/generic/nsBlockFrame.h
@@ -396,11 +396,6 @@ protected:
                    bool*        aInOverflowLines,
                    FrameLines** aOverflowLines);
 
-  void SetFlags(nsFrameState aFlags) {
-    mState &= ~NS_BLOCK_FLAGS_MASK;
-    mState |= aFlags;
-  }
-
   /** move the frames contained by aLine by aDeltaBCoord
     * if aLine is a block, its child floats are added to the state manager
     */
diff --git a/layout/mathml/nsMathMLContainerFrame.cpp b/layout/mathml/nsMathMLContainerFrame.cpp
index fcf2576d0f47..ad1b13efded8 100644
--- a/layout/mathml/nsMathMLContainerFrame.cpp
+++ b/layout/mathml/nsMathMLContainerFrame.cpp
@@ -1583,12 +1583,9 @@ nsMathMLContainerFrame::ReportInvalidChildError(nsIAtom* aChildTag)
 //==========================
 
 nsContainerFrame*
-NS_NewMathMLmathBlockFrame(nsIPresShell* aPresShell, nsStyleContext* aContext,
-                           nsFrameState aFlags)
+NS_NewMathMLmathBlockFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 {
-  nsMathMLmathBlockFrame* it = new (aPresShell) nsMathMLmathBlockFrame(aContext);
-  it->SetFlags(aFlags);
-  return it;
+  return new (aPresShell) nsMathMLmathBlockFrame(aContext);
 }
 
 NS_IMPL_FRAMEARENA_HELPERS(nsMathMLmathBlockFrame)
diff --git a/layout/mathml/nsMathMLContainerFrame.h b/layout/mathml/nsMathMLContainerFrame.h
index 53599f401cee..be71e00cc87d 100644
--- a/layout/mathml/nsMathMLContainerFrame.h
+++ b/layout/mathml/nsMathMLContainerFrame.h
@@ -418,7 +418,7 @@ public:
   NS_DECL_FRAMEARENA_HELPERS
 
   friend nsContainerFrame* NS_NewMathMLmathBlockFrame(nsIPresShell* aPresShell,
-          nsStyleContext* aContext, nsFrameState aFlags);
+          nsStyleContext* aContext);
 
   // beware, mFrames is not set by nsBlockFrame
   // cannot use mFrames{.FirstChild()|.etc} since the block code doesn't set mFrames
@@ -481,7 +481,8 @@ protected:
   explicit nsMathMLmathBlockFrame(nsStyleContext* aContext) : nsBlockFrame(aContext) {
     // We should always have a float manager.  Not that things can really try
     // to float out of us anyway, but we need one for line layout.
-    AddStateBits(NS_BLOCK_FLOAT_MGR);
+    // Bug 1301881: Do we still need to set NS_BLOCK_FLOAT_MGR?
+    // AddStateBits(NS_BLOCK_FLOAT_MGR);
   }
   virtual ~nsMathMLmathBlockFrame() {}
 };
diff --git a/layout/mathml/nsMathMLParts.h b/layout/mathml/nsMathMLParts.h
index c3907e6696ca..5d4285ee9093 100644
--- a/layout/mathml/nsMathMLParts.h
+++ b/layout/mathml/nsMathMLParts.h
@@ -36,10 +36,6 @@ nsIFrame* NS_NewMathMLmactionFrame(nsIPresShell* aPresShell, nsStyleContext* aCo
 nsIFrame* NS_NewMathMLmencloseFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
 nsIFrame* NS_NewMathMLsemanticsFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
 
-nsContainerFrame* NS_NewMathMLmathBlockFrame(nsIPresShell* aPresShell, nsStyleContext* aContext, nsFrameState aFlags);
+nsContainerFrame* NS_NewMathMLmathBlockFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
 nsContainerFrame* NS_NewMathMLmathInlineFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
-inline nsContainerFrame* NS_CreateNewMathMLmathBlockFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
-{
-  return NS_NewMathMLmathBlockFrame(aPresShell, aContext, nsFrameState(0));
-}
 #endif /* nsMathMLParts_h___ */
diff --git a/layout/xul/nsXULLabelFrame.cpp b/layout/xul/nsXULLabelFrame.cpp
index 26619b1810a9..22b8754617c6 100644
--- a/layout/xul/nsXULLabelFrame.cpp
+++ b/layout/xul/nsXULLabelFrame.cpp
@@ -16,8 +16,8 @@ nsIFrame*
 NS_NewXULLabelFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 {
   nsXULLabelFrame* it = new (aPresShell) nsXULLabelFrame(aContext);
-  
-  it->SetFlags(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+
+  it->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
 
   return it;
 }