--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -4949,17 +4949,17 @@ nsCSSFrameConstructor::ConstructNonScrol
   bool clipPaginatedOverflow =
     (aItem.mFCData->mBits & FCDATA_FORCED_NON_SCROLLABLE_BLOCK) != 0;
   nsFrameState flags = nsFrameState(0);
   if ((aDisplay->IsAbsolutelyPositionedStyle() ||
        aDisplay->IsFloatingStyle() ||
        StyleDisplay::InlineBlock == aDisplay->mDisplay ||
        clipPaginatedOverflow) &&
       !aParentFrame->IsSVGText()) {
-    flags = NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT;
+    flags = NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS;
     if (clipPaginatedOverflow) {
       flags |= NS_BLOCK_CLIP_PAGINATED_OVERFLOW;
     }
   }
 
   nsContainerFrame* newFrame = aConstructor(mPresShell, styleContext);
   newFrame->AddStateBits(flags);
   ConstructBlock(aState, aItem.mContent,
@@ -5122,17 +5122,17 @@ nsCSSFrameConstructor::FlushAccumulatedB
     ResolveAnonymousBoxStyle(anonPseudo, parentContext);
 
 
   // then, create a block frame that will wrap the child frames. Make it a
   // MathML frame so that Get(Absolute/Float)ContainingBlockFor know that this
   // is not a suitable block.
   nsContainerFrame* blockFrame =
     NS_NewMathMLmathBlockFrame(mPresShell, blockContext);
-  blockFrame->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+  blockFrame->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
 
   InitAndRestoreFrame(aState, aContent, aParentFrame, blockFrame);
   ReparentFrames(this, blockFrame, aBlockItems);
   // abs-pos and floats are disabled in MathML children so we don't have to
   // worry about messing up those.
   blockFrame->SetInitialChildList(kPrincipalList, aBlockItems);
   NS_ASSERTION(aBlockItems.IsEmpty(), "What happened?");
   aBlockItems.Clear();

--- a/layout/forms/nsLegendFrame.cpp
+++ b/layout/forms/nsLegendFrame.cpp
@@ -17,19 +17,17 @@ NS_NewLegendFrame(nsIPresShell* aPresShe
 {
 #ifdef DEBUG
   const nsStyleDisplay* disp = aContext->StyleDisplay();
   NS_ASSERTION(!disp->IsAbsolutelyPositionedStyle() && !disp->IsFloatingStyle(),
                "Legends should not be positioned and should not float");
 #endif
 
   nsIFrame* f = new (aPresShell) nsLegendFrame(aContext);
-  if (f) {
-    f->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
-  }
+  f->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   return f;
 }
 
 NS_IMPL_FRAMEARENA_HELPERS(nsLegendFrame)
 
 nsIAtom*
 nsLegendFrame::GetType() const
 {

--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -301,17 +301,17 @@ NS_NewBlockFrame(nsIPresShell* aPresShel
   return new (aPresShell) nsBlockFrame(aContext);
 }
 
 nsBlockFrame*
 NS_NewBlockFormattingContext(nsIPresShell* aPresShell,
                              nsStyleContext* aStyleContext)
 {
   nsBlockFrame* blockFrame = NS_NewBlockFrame(aPresShell, aStyleContext);
-  blockFrame->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+  blockFrame->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   return blockFrame;
 }
 
 NS_IMPL_FRAMEARENA_HELPERS(nsBlockFrame)
 
 nsBlockFrame::~nsBlockFrame()
 {
 }
@@ -6914,17 +6914,17 @@ nsBlockFrame::Init(nsIContent*       aCo
   //   formatting context.
   // (http://dev.w3.org/csswg/css-writing-modes/#block-flow)
   // If the box has contain: paint (or contain: strict), then it should also
   // establish a formatting context.
   if (StyleDisplay()->mDisplay == mozilla::StyleDisplay::FlowRoot ||
       (GetParent() && StyleVisibility()->mWritingMode !=
                       GetParent()->StyleVisibility()->mWritingMode) ||
       StyleDisplay()->IsContainPaint()) {
-    AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
+    AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   }
 
   if ((GetStateBits() &
        (NS_FRAME_FONT_INFLATION_CONTAINER | NS_BLOCK_FLOAT_MGR)) ==
       (NS_FRAME_FONT_INFLATION_CONTAINER | NS_BLOCK_FLOAT_MGR)) {
     AddStateBits(NS_FRAME_FONT_INFLATION_FLOW_ROOT);
   }
 }

--- a/layout/generic/nsFrameStateBits.h
+++ b/layout/generic/nsFrameStateBits.h
@@ -478,16 +478,19 @@ FRAME_STATE_BIT(Block, 21, NS_BLOCK_HAS_
 // mIsBStartMarginRoot and mIsBEndMarginRoot flags.
 FRAME_STATE_BIT(Block, 22, NS_BLOCK_MARGIN_ROOT)
 
 // This indicates that a block frame should create its own float manager. This
 // is required by each block frame that can contain floats. The float manager is
 // used to reserve space for the floated frames.
 FRAME_STATE_BIT(Block, 23, NS_BLOCK_FLOAT_MGR)
 
+// For setting the relevant bits on a block formatting context:
+#define NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS (NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT)
+
 FRAME_STATE_BIT(Block, 24, NS_BLOCK_HAS_LINE_CURSOR)
 
 FRAME_STATE_BIT(Block, 25, NS_BLOCK_HAS_OVERFLOW_LINES)
 
 FRAME_STATE_BIT(Block, 26, NS_BLOCK_HAS_OVERFLOW_OUT_OF_FLOWS)
 
 // Set on any block that has descendant frames in the normal
 // flow with 'clear' set to something other than 'none'

--- a/layout/generic/nsHTMLParts.h
+++ b/layout/generic/nsHTMLParts.h
@@ -25,18 +25,17 @@ class nsIChannel;
 class nsTableColFrame;
 namespace mozilla {
 class ViewportFrame;
 } // namespace mozilla
 
 // These are all the block specific frame bits, they are copied from
 // the prev-in-flow to a newly created next-in-flow, except for the
 // NS_BLOCK_FLAGS_NON_INHERITED_MASK bits below.
-#define NS_BLOCK_FLAGS_MASK (NS_BLOCK_MARGIN_ROOT              | \
-                             NS_BLOCK_FLOAT_MGR                | \
+#define NS_BLOCK_FLAGS_MASK (NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS | \
                              NS_BLOCK_CLIP_PAGINATED_OVERFLOW  | \
                              NS_BLOCK_HAS_FIRST_LETTER_STYLE   | \
                              NS_BLOCK_FRAME_HAS_OUTSIDE_BULLET | \
                              NS_BLOCK_HAS_FIRST_LETTER_CHILD   | \
                              NS_BLOCK_FRAME_HAS_INSIDE_BULLET)
 
 // This is the subset of NS_BLOCK_FLAGS_MASK that is NOT inherited
 // by default.  They should only be set on the first-in-flow.

--- a/layout/xul/nsXULLabelFrame.cpp
+++ b/layout/xul/nsXULLabelFrame.cpp
@@ -11,19 +11,17 @@
 #include "nsNameSpaceManager.h"
 
 using namespace mozilla;
 
 nsIFrame*
 NS_NewXULLabelFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 {
   nsXULLabelFrame* it = new (aPresShell) nsXULLabelFrame(aContext);
-
-  it->AddStateBits(NS_BLOCK_FLOAT_MGR | NS_BLOCK_MARGIN_ROOT);
-
+  it->AddStateBits(NS_BLOCK_FORMATTING_CONTEXT_STATE_BITS);
   return it;
 }
 
 NS_IMPL_FRAMEARENA_HELPERS(nsXULLabelFrame)
 
 // If you make changes to this function, check its counterparts 
 // in nsBoxFrame and nsTextBoxFrame
 nsresult