--- a/dom/html/HTMLBRElement.cpp
+++ b/dom/html/HTMLBRElement.cpp
@@ -25,20 +25,20 @@ HTMLBRElement::HTMLBRElement(already_Add
 
 HTMLBRElement::~HTMLBRElement()
 {
 }
 
 NS_IMPL_ELEMENT_CLONE(HTMLBRElement)
 
 static const nsAttrValue::EnumTable kClearTable[] = {
-  { "left", NS_STYLE_CLEAR_LEFT },
-  { "right", NS_STYLE_CLEAR_RIGHT },
-  { "all", NS_STYLE_CLEAR_BOTH },
-  { "both", NS_STYLE_CLEAR_BOTH },
+  { "left", StyleClear::Left },
+  { "right", StyleClear::Right },
+  { "all", StyleClear::Both },
+  { "both", StyleClear::Both },
   { nullptr, 0 }
 };
 
 bool
 HTMLBRElement::ParseAttribute(int32_t aNamespaceID,
                               nsIAtom* aAttribute,
                               const nsAString& aValue,
                               nsAttrValue& aResult)

--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -3045,41 +3045,44 @@ nsLayoutUtils::TranslateViewToWidget(nsP
   nsPoint pt = (aPt +
   viewOffset).ApplyResolution(GetCurrentAPZResolutionScale(aPresContext->PresShell()));
   LayoutDeviceIntPoint relativeToViewWidget(aPresContext->AppUnitsToDevPixels(pt.x),
                                             aPresContext->AppUnitsToDevPixels(pt.y));
   return relativeToViewWidget + WidgetToWidgetOffset(viewWidget, aWidget);
 }
 
 // Combine aNewBreakType with aOrigBreakType, but limit the break types
-// to NS_STYLE_CLEAR_LEFT, RIGHT, BOTH.
-uint8_t
-nsLayoutUtils::CombineBreakType(uint8_t aOrigBreakType,
-                                uint8_t aNewBreakType)
-{
-  uint8_t breakType = aOrigBreakType;
+// to StyleClear::Left, Right, Both.
+StyleClear
+nsLayoutUtils::CombineBreakType(StyleClear aOrigBreakType,
+                                StyleClear aNewBreakType)
+{
+  StyleClear breakType = aOrigBreakType;
   switch(breakType) {
-  case NS_STYLE_CLEAR_LEFT:
-    if (NS_STYLE_CLEAR_RIGHT == aNewBreakType ||
-        NS_STYLE_CLEAR_BOTH == aNewBreakType) {
-      breakType = NS_STYLE_CLEAR_BOTH;
-    }
-    break;
-  case NS_STYLE_CLEAR_RIGHT:
-    if (NS_STYLE_CLEAR_LEFT == aNewBreakType ||
-        NS_STYLE_CLEAR_BOTH == aNewBreakType) {
-      breakType = NS_STYLE_CLEAR_BOTH;
-    }
-    break;
-  case NS_STYLE_CLEAR_NONE:
-    if (NS_STYLE_CLEAR_LEFT == aNewBreakType ||
-        NS_STYLE_CLEAR_RIGHT == aNewBreakType ||
-        NS_STYLE_CLEAR_BOTH == aNewBreakType) {
-      breakType = aNewBreakType;
-    }
+    case StyleClear::Left:
+      if (StyleClear::Right == aNewBreakType ||
+          StyleClear::Both == aNewBreakType) {
+        breakType = StyleClear::Both;
+      }
+      break;
+    case StyleClear::Right:
+      if (StyleClear::Left == aNewBreakType ||
+          StyleClear::Both == aNewBreakType) {
+        breakType = StyleClear::Both;
+      }
+      break;
+    case StyleClear::None_:
+      if (StyleClear::Left == aNewBreakType ||
+          StyleClear::Right == aNewBreakType ||
+          StyleClear::Both == aNewBreakType) {
+        breakType = aNewBreakType;
+      }
+      break;
+    default:
+      break;
   }
   return breakType;
 }
 
 #ifdef MOZ_DUMP_PAINTING
 #include <stdio.h>
 
 static bool gDumpEventList = false;

--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -689,18 +689,19 @@ public:
 
   /**
    * If this frame is a placeholder for a float, then return the float,
    * otherwise return nullptr.  aPlaceholder must be a placeholder frame.
    */
   static nsIFrame* GetFloatFromPlaceholder(nsIFrame* aPlaceholder);
 
   // Combine aNewBreakType with aOrigBreakType, but limit the break types
-  // to NS_STYLE_CLEAR_LEFT, RIGHT, LEFT_AND_RIGHT.
-  static uint8_t CombineBreakType(uint8_t aOrigBreakType, uint8_t aNewBreakType);
+  // to StyleClear::Left, Right, Both.
+  static mozilla::StyleClear CombineBreakType(mozilla::StyleClear aOrigBreakType,
+                                              mozilla::StyleClear aNewBreakType);
 
   /**
    * Get the coordinates of a given DOM mouse event, relative to a given
    * frame. Works only for DOM events generated by WidgetGUIEvents.
    * @param aDOMEvent the event
    * @param aFrame the frame to make coordinates relative to
    * @return the point, or (NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE) if
    * for some reason the coordinates for the mouse are not known (e.g.,

--- a/layout/generic/BlockReflowInput.cpp
+++ b/layout/generic/BlockReflowInput.cpp
@@ -39,17 +39,17 @@ BlockReflowInput::BlockReflowInput(const
     mPresContext(aPresContext),
     mReflowInput(aReflowInput),
     mContentArea(aReflowInput.GetWritingMode()),
     mPushedFloats(nullptr),
     mOverflowTracker(nullptr),
     mBorderPadding(mReflowInput.ComputedLogicalBorderPadding()),
     mPrevBEndMargin(),
     mLineNumber(0),
-    mFloatBreakType(NS_STYLE_CLEAR_NONE),
+    mFloatBreakType(StyleClear::None_),
     mConsumedBSize(aConsumedBSize)
 {
   if (!sFloatFragmentsInsideColumnPrefCached) {
     sFloatFragmentsInsideColumnPrefCached = true;
     Preferences::AddBoolVarCache(&sFloatFragmentsInsideColumnEnabled,
                                  "layout.float-fragments-inside-column.enabled");
   }
   mFlags.mFloatFragmentsInsideColumnEnabled = sFloatFragmentsInsideColumnEnabled;
@@ -727,17 +727,17 @@ BlockReflowInput::FlowAndPlaceFloat(nsIF
 
   // Enforce CSS2 9.5.1 rule [2], i.e., make sure that a float isn't
   // ``above'' another float that preceded it in the flow.
   mBCoord = std::max(mFloatManager->GetLowestFloatTop(), mBCoord);
 
   // See if the float should clear any preceding floats...
   // XXX We need to mark this float somehow so that it gets reflowed
   // when floats are inserted before it.
-  if (NS_STYLE_CLEAR_NONE != floatDisplay->mBreakType) {
+  if (StyleClear::None_ != floatDisplay->mBreakType) {
     // XXXldb Does this handle vertical margins correctly?
     mBCoord = ClearFloats(mBCoord, floatDisplay->PhysicalBreakType(wm));
   }
     // Get the band of available space
   nsFlowAreaRect floatAvailableSpace = GetFloatAvailableSpace(mBCoord);
   LogicalRect adjustedAvailableSpace =
     mBlock->AdjustFloatAvailableSpace(*this, floatAvailableSpace.mRect, aFloat);
 
@@ -1075,40 +1075,40 @@ BlockReflowInput::PlaceBelowCurrentLineF
       delete fc;
       aLine->SetHadFloatPushed();
     }
     fc = next;
   }
 }
 
 nscoord
-BlockReflowInput::ClearFloats(nscoord aBCoord, uint8_t aBreakType,
+BlockReflowInput::ClearFloats(nscoord aBCoord, StyleClear aBreakType,
                                 nsIFrame *aReplacedBlock,
                                 uint32_t aFlags)
 {
 #ifdef DEBUG
   if (nsBlockFrame::gNoisyReflow) {
     nsFrame::IndentBy(stdout, nsBlockFrame::gNoiseIndent);
     printf("clear floats: in: aBCoord=%d\n", aBCoord);
   }
 #endif
 
 #ifdef NOISY_FLOAT_CLEARING
-  printf("BlockReflowInput::ClearFloats: aBCoord=%d breakType=%d\n",
-         aBCoord, aBreakType);
+  printf("BlockReflowInput::ClearFloats: aBCoord=%d breakType=%s\n",
+         aBCoord, nsLineBox::BreakTypeToString(aBreakType));
   mFloatManager->List(stdout);
 #endif
 
   if (!mFloatManager->HasAnyFloats()) {
     return aBCoord;
   }
 
   nscoord newBCoord = aBCoord;
 
-  if (aBreakType != NS_STYLE_CLEAR_NONE) {
+  if (aBreakType != StyleClear::None_) {
     newBCoord = mFloatManager->ClearFloats(newBCoord, aBreakType, aFlags);
   }
 
   if (aReplacedBlock) {
     for (;;) {
       nsFlowAreaRect floatAvailableSpace = GetFloatAvailableSpace(newBCoord);
       if (ReplacedBlockFitsInAvailSpace(aReplacedBlock, floatAvailableSpace)) {
         break;

--- a/layout/generic/BlockReflowInput.h
+++ b/layout/generic/BlockReflowInput.h
@@ -144,17 +144,17 @@ public:
   bool FlowAndPlaceFloat(nsIFrame* aFloat);
 
   void PlaceBelowCurrentLineFloats(nsFloatCacheFreeList& aFloats,
                                    nsLineBox* aLine);
 
   // Returns the first coordinate >= aBCoord that clears the
   // floats indicated by aBreakType and has enough inline size between floats
   // (or no floats remaining) to accomodate aReplacedBlock.
-  nscoord ClearFloats(nscoord aBCoord, uint8_t aBreakType,
+  nscoord ClearFloats(nscoord aBCoord, mozilla::StyleClear aBreakType,
                       nsIFrame *aReplacedBlock = nullptr,
                       uint32_t aFlags = 0);
 
   // Advances to the next band, i.e., the next horizontal stripe in
   // which there is a different set of floats.
   // Return false if it did not advance, which only happens for
   // constrained heights (and means that we should get pushed to the
   // next column/page).
@@ -366,17 +366,17 @@ public:
   nsFloatCacheFreeList mBelowCurrentLineFloats;
 
   nscoord mMinLineHeight;
 
   int32_t mLineNumber;
 
   Flags mFlags;
 
-  uint8_t mFloatBreakType;
+  StyleClear mFloatBreakType;
 
   // The amount of computed block-direction size "consumed" by previous-in-flows.
   nscoord mConsumedBSize;
 
 private:
   bool CanPlaceFloat(nscoord aFloatISize,
                      const nsFlowAreaRect& aFloatAvailableSpace);
 

--- a/layout/generic/WritingModes.h
+++ b/layout/generic/WritingModes.h
@@ -2009,24 +2009,25 @@ nsStyleDisplay::PhysicalFloats(mozilla::
     return aWM.IsBidiLTR() ? StyleFloat::Left : StyleFloat::Right;
   }
   if (mFloat == StyleFloat::InlineEnd) {
     return aWM.IsBidiLTR() ? StyleFloat::Right : StyleFloat::Left;
   }
   return mFloat;
 }
 
-inline uint8_t
+inline mozilla::StyleClear
 nsStyleDisplay::PhysicalBreakType(mozilla::WritingMode aWM) const
 {
-  if (mBreakType == NS_STYLE_CLEAR_INLINE_START) {
-    return aWM.IsBidiLTR() ? NS_STYLE_CLEAR_LEFT : NS_STYLE_CLEAR_RIGHT;
+  using StyleClear = mozilla::StyleClear;
+  if (mBreakType == StyleClear::InlineStart) {
+    return aWM.IsBidiLTR() ? StyleClear::Left : StyleClear::Right;
   }
-  if (mBreakType == NS_STYLE_CLEAR_INLINE_END) {
-    return aWM.IsBidiLTR() ? NS_STYLE_CLEAR_RIGHT : NS_STYLE_CLEAR_LEFT;
+  if (mBreakType == StyleClear::InlineEnd) {
+    return aWM.IsBidiLTR() ? StyleClear::Right : StyleClear::Left;
   }
   return mBreakType;
 }
 
 inline bool
 nsStyleMargin::HasBlockAxisAuto(mozilla::WritingMode aWM) const
 {
   return mMargin.HasBlockAxisAuto(aWM);

--- a/layout/generic/nsBRFrame.cpp
+++ b/layout/generic/nsBRFrame.cpp
@@ -139,19 +139,19 @@ BRFrame::Reflow(nsPresContext* aPresCont
       // XXX This also fixes bug 10036!
       // Warning: nsTextControlFrame::CalculateSizeStandard depends on
       // the following line, see bug 228752.
       // The code below in AddInlinePrefISize also adds 1 appunit to width
       finalSize.ISize(wm) = 1;
     }
 
     // Return our reflow status
-    uint32_t breakType = aReflowInput.mStyleDisplay->PhysicalBreakType(wm);
-    if (NS_STYLE_CLEAR_NONE == breakType) {
-      breakType = NS_STYLE_CLEAR_LINE;
+    StyleClear breakType = aReflowInput.mStyleDisplay->PhysicalBreakType(wm);
+    if (StyleClear::None_ == breakType) {
+      breakType = StyleClear::Line;
     }
 
     aStatus = NS_INLINE_BREAK | NS_INLINE_BREAK_AFTER |
       NS_INLINE_MAKE_BREAK_TYPE(breakType);
     ll->SetLineEndsInBR(true);
   }
   else {
     aStatus = NS_FRAME_COMPLETE;

--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -1544,17 +1544,17 @@ nsBlockFrame::ComputeFinalSize(const Ref
         std::min(blockEndEdgeOfChildren + aState.mPrevBEndMargin.get(),
                aState.mReflowInput.AvailableBSize());
     }
   }
   if (aState.mFlags.mBlockNeedsFloatManager) {
     // Include the float manager's state to properly account for the
     // block-end margin of any floated elements; e.g., inside a table cell.
     nscoord floatHeight =
-      aState.ClearFloats(blockEndEdgeOfChildren, NS_STYLE_CLEAR_BOTH,
+      aState.ClearFloats(blockEndEdgeOfChildren, StyleClear::Both,
                          nullptr, nsFloatManager::DONT_CLEAR_PUSHED_FLOATS);
     blockEndEdgeOfChildren = std::max(blockEndEdgeOfChildren, floatHeight);
   }
 
   if (NS_UNCONSTRAINEDSIZE != aReflowInput.ComputedBSize()
       && (GetParent()->GetType() != nsGkAtoms::columnSetFrame ||
           aReflowInput.mParentReflowInput->AvailableBSize() == NS_UNCONSTRAINEDSIZE)) {
     ComputeFinalBSize(aReflowInput, &aState.mReflowStatus,
@@ -1914,24 +1914,25 @@ nsBlockFrame::PrepareResizeReflow(BlockR
       if (!line->IsBlock()) {
         printf("PrepareResizeReflow thinks line %p is %simpacted by floats\n", 
                line.get(), line->IsImpactedByFloat() ? "" : "not ");
       }
 #endif
 #ifdef DEBUG
       if (gNoisyReflow && !line->IsDirty()) {
         IndentBy(stdout, gNoiseIndent + 1);
-        printf("skipped: line=%p next=%p %s %s%s%s breakTypeBefore/After=%d/%d xmost=%d\n",
+        printf("skipped: line=%p next=%p %s %s%s%s breakTypeBefore/After=%s/%s xmost=%d\n",
            static_cast<void*>(line.get()),
            static_cast<void*>((line.next() != end_lines() ? line.next().get() : nullptr)),
            line->IsBlock() ? "block" : "inline",
            line->HasBreakAfter() ? "has-break-after " : "",
            line->HasFloats() ? "has-floats " : "",
            line->IsImpactedByFloat() ? "impacted " : "",
-           line->GetBreakTypeBefore(), line->GetBreakTypeAfter(),
+           line->BreakTypeToString(line->GetBreakTypeBefore()),
+           line->BreakTypeToString(line->GetBreakTypeAfter()),
            line->IEnd());
       }
 #endif
     }
   }
   else {
     // Mark everything dirty
     for (line_iterator line = begin_lines(), line_end = end_lines();
@@ -2024,17 +2025,17 @@ nsBlockFrame::PropagateFloatDamage(Block
         aLine->MarkDirty();
       }
     }
   }
 }
 
 static bool LineHasClear(nsLineBox* aLine) {
   return aLine->IsBlock()
-    ? (aLine->GetBreakTypeBefore() ||
+    ? (aLine->GetBreakTypeBefore() != StyleClear::None_ ||
        (aLine->mFirstChild->GetStateBits() & NS_BLOCK_HAS_CLEAR_CHILDREN) ||
        !nsBlockFrame::BlockCanIntersectFloats(aLine->mFirstChild))
     : aLine->HasFloatBreakAfter();
 }
 
 
 /**
  * Reparent a whole list of floats from aOldParent to this block.  The
@@ -2075,17 +2076,17 @@ static void DumpLine(const BlockReflowIn
 #endif
 }
 
 void
 nsBlockFrame::ReflowDirtyLines(BlockReflowInput& aState)
 {
   bool keepGoing = true;
   bool repositionViews = false; // should we really need this?
-  bool foundAnyClears = aState.mFloatBreakType != NS_STYLE_CLEAR_NONE;
+  bool foundAnyClears = aState.mFloatBreakType != StyleClear::None_;
   bool willReflowAgain = false;
 
 #ifdef DEBUG
   if (gNoisyReflow) {
     IndentBy(stdout, gNoiseIndent);
     ListTag(stdout);
     printf(": reflowing dirty lines");
     printf(" computedISize=%d\n", aState.mReflowInput.ComputedISize());
@@ -2116,17 +2117,17 @@ nsBlockFrame::ReflowDirtyLines(BlockRefl
     // recompute the carried out margin before the line if we want to
     // reflow it or if its previous margin is dirty
   bool needToRecoverState = false;
     // Float continuations were reflowed in ReflowPushedFloats
   bool reflowedFloat = mFloats.NotEmpty() &&
     (mFloats.FirstChild()->GetStateBits() & NS_FRAME_IS_PUSHED_FLOAT);
   bool lastLineMovedUp = false;
   // We save up information about BR-clearance here
-  uint8_t inlineFloatBreakType = aState.mFloatBreakType;
+  StyleClear inlineFloatBreakType = aState.mFloatBreakType;
 
   line_iterator line = begin_lines(), line_end = end_lines();
 
   // Reflow the lines that are already ours
   for ( ; line != line_end; ++line, aState.AdvanceToNextLine()) {
     DumpLine(aState, line, deltaBCoord, 0);
 #ifdef DEBUG
     AutoNoisyIndenter indent2(gNoisyReflow);
@@ -2147,22 +2148,22 @@ nsBlockFrame::ReflowDirtyLines(BlockRefl
     if (line->IsBlock() &&
         !nsBlockFrame::BlockCanIntersectFloats(line->mFirstChild)) {
       replacedBlock = line->mFirstChild;
     }
 
     // We have to reflow the line if it's a block whose clearance
     // might have changed, so detect that.
     if (!line->IsDirty() &&
-        (line->GetBreakTypeBefore() != NS_STYLE_CLEAR_NONE ||
+        (line->GetBreakTypeBefore() != StyleClear::None_ ||
          replacedBlock)) {
       nscoord curBCoord = aState.mBCoord;
       // See where we would be after applying any clearance due to
       // BRs.
-      if (inlineFloatBreakType != NS_STYLE_CLEAR_NONE) {
+      if (inlineFloatBreakType != StyleClear::None_) {
         curBCoord = aState.ClearFloats(curBCoord, inlineFloatBreakType);
       }
 
       nscoord newBCoord =
         aState.ClearFloats(curBCoord, line->GetBreakTypeBefore(), replacedBlock);
 
       if (line->HasClearance()) {
         // Reflow the line if it might not have clearance anymore.
@@ -2178,24 +2179,24 @@ nsBlockFrame::ReflowDirtyLines(BlockRefl
         // Reflow the line if the line might have clearance now.
         if (curBCoord != newBCoord) {
           line->MarkDirty();
         }
       }
     }
 
     // We might have to reflow a line that is after a clearing BR.
-    if (inlineFloatBreakType != NS_STYLE_CLEAR_NONE) {
+    if (inlineFloatBreakType != StyleClear::None_) {
       aState.mBCoord = aState.ClearFloats(aState.mBCoord, inlineFloatBreakType);
       if (aState.mBCoord != line->BStart() + deltaBCoord) {
         // SlideLine is not going to put the line where the clearance
         // put it. Reflow the line to be sure.
         line->MarkDirty();
       }
-      inlineFloatBreakType = NS_STYLE_CLEAR_NONE;
+      inlineFloatBreakType = StyleClear::None_;
     }
 
     bool previousMarginWasDirty = line->IsPreviousMarginDirty();
     if (previousMarginWasDirty) {
       // If the previous margin is dirty, reflow the current line
       line->MarkDirty();
       line->ClearPreviousMarginDirty();
     } else if (line->BEnd() + deltaBCoord > aState.mBEndEdge) {
@@ -2438,17 +2439,17 @@ nsBlockFrame::ReflowDirtyLines(BlockRefl
       // sure whether we really want to mark all lines dirty after an
       // interrupt, but until we get better at propagating float damage we
       // really do need to do it this way; see comments inside MarkLineDirty.
       MarkLineDirtyForInterrupt(line);
     }
   }
 
   // Handle BR-clearance from the last line of the block
-  if (inlineFloatBreakType != NS_STYLE_CLEAR_NONE) {
+  if (inlineFloatBreakType != StyleClear::None_) {
     aState.mBCoord = aState.ClearFloats(aState.mBCoord, inlineFloatBreakType);
   }
 
   if (needToRecoverState) {
     // Is this expensive?
     aState.ReconstructMarginBefore(line);
 
     // Update aState.mPrevChild as if we had reflowed all of the frames in
@@ -3121,22 +3122,22 @@ nsBlockFrame::ReflowBlockFrame(BlockRefl
   if (!frame) {
     NS_ASSERTION(false, "program error - unexpected empty line"); 
     return; 
   }
 
   // Prepare the block reflow engine
   nsBlockReflowContext brc(aState.mPresContext, aState.mReflowInput);
 
-  uint8_t breakType = frame->StyleDisplay()->
+  StyleClear breakType = frame->StyleDisplay()->
     PhysicalBreakType(aState.mReflowInput.GetWritingMode());
-  if (NS_STYLE_CLEAR_NONE != aState.mFloatBreakType) {
+  if (StyleClear::None_ != aState.mFloatBreakType) {
     breakType = nsLayoutUtils::CombineBreakType(breakType,
                                                 aState.mFloatBreakType);
-    aState.mFloatBreakType = NS_STYLE_CLEAR_NONE;
+    aState.mFloatBreakType = StyleClear::None_;
   }
 
   // Clear past floats before the block if the clear style is not none
   aLine->SetBreakTypeBefore(breakType);
 
   // See if we should apply the block-start margin. If the block frame being
   // reflowed is a continuation (non-null prev-in-flow) then we don't
   // apply its block-start margin because it's not significant unless it has
@@ -3149,17 +3150,17 @@ nsBlockFrame::ReflowBlockFrame(BlockRefl
     // The HasClearance setting is only valid if ShouldApplyBStartMargin
     // returned false (in which case the block-start margin-root set our
     // clearance flag). Otherwise clear it now. We'll set it later on
     // ourselves if necessary.
     aLine->ClearHasClearance();
   }
   bool treatWithClearance = aLine->HasClearance();
 
-  bool mightClearFloats = breakType != NS_STYLE_CLEAR_NONE;
+  bool mightClearFloats = breakType != StyleClear::None_;
   nsIFrame *replacedBlock = nullptr;
   if (!nsBlockFrame::BlockCanIntersectFloats(frame)) {
     mightClearFloats = true;
     replacedBlock = frame;
   }
 
   // If our block-start margin was counted as part of some parent's block-start
   // margin collapse, and we are being speculatively reflowed assuming this
@@ -3428,17 +3429,17 @@ nsBlockFrame::ReflowBlockFrame(BlockRefl
                                                 floatAvailableSpace)) {
         // Advance to the next band.
         nscoord newBCoord = aState.mBCoord;
         if (aState.AdvanceToNextBand(floatAvailableSpace.mRect, &newBCoord)) {
           advanced = true;
         }
         // ClearFloats might be able to advance us further once we're there.
         aState.mBCoord =
-          aState.ClearFloats(newBCoord, NS_STYLE_CLEAR_NONE, replacedBlock);
+          aState.ClearFloats(newBCoord, StyleClear::None_, replacedBlock);
         // Start over with a new available space rect at the new height.
         floatAvailableSpace =
           aState.GetFloatAvailableSpaceWithState(aState.mBCoord,
                                                  &floatManagerState);
       }
 
       LogicalRect oldAvailSpace(availSpace);
       aState.ComputeBlockAvailSpace(frame, floatAvailableSpace,
@@ -4049,17 +4050,17 @@ nsBlockFrame::DoReflowInlineFrames(Block
 }
 
 /**
  * Reflow an inline frame. The reflow status is mapped from the frames
  * reflow status to the lines reflow status (not to our reflow status).
  * The line reflow status is simple: true means keep placing frames
  * on the line; false means don't (the line is done). If the line
  * has some sort of breaking affect then aLine's break-type will be set
- * to something other than NS_STYLE_CLEAR_NONE.
+ * to something other than StyleClear::None_.
  */
 void
 nsBlockFrame::ReflowInlineFrame(BlockReflowInput& aState,
                                 nsLineLayout& aLineLayout,
                                 line_iterator aLine,
                                 nsIFrame* aFrame,
                                 LineReflowStatus* aLineReflowStatus)
 {
@@ -4106,28 +4107,27 @@ nsBlockFrame::ReflowInlineFrame(BlockRef
       see bug 22496
    */
 
   // Process the child frames reflow status. There are 5 cases:
   // complete, not-complete, break-before, break-after-complete,
   // break-after-not-complete. There are two situations: we are a
   // block or we are an inline. This makes a total of 10 cases
   // (fortunately, there is some overlap).
-  aLine->SetBreakTypeAfter(NS_STYLE_CLEAR_NONE);
-  if (NS_INLINE_IS_BREAK(frameReflowStatus) || 
-      (NS_STYLE_CLEAR_NONE != aState.mFloatBreakType)) {
+  aLine->SetBreakTypeAfter(StyleClear::None_);
+  if (NS_INLINE_IS_BREAK(frameReflowStatus) ||
+      StyleClear::None_ != aState.mFloatBreakType) {
     // Always abort the line reflow (because a line break is the
     // minimal amount of break we do).
     *aLineReflowStatus = LINE_REFLOW_STOP;
 
     // XXX what should aLine's break-type be set to in all these cases?
-    uint8_t breakType = NS_INLINE_GET_BREAK_TYPE(frameReflowStatus);
-    NS_ASSERTION((NS_STYLE_CLEAR_NONE != breakType) || 
-                 (NS_STYLE_CLEAR_NONE != aState.mFloatBreakType), "bad break type");
-    NS_ASSERTION(NS_STYLE_CLEAR_MAX >= breakType, "invalid break type");
+    StyleClear breakType = NS_INLINE_GET_BREAK_TYPE(frameReflowStatus);
+    NS_ASSERTION(StyleClear::None_ != breakType ||
+                 StyleClear::None_ != aState.mFloatBreakType, "bad break type");
 
     if (NS_INLINE_IS_BREAK_BEFORE(frameReflowStatus)) {
       // Break-before cases.
       if (aFrame == aLine->mFirstChild) {
         // If we break before the first frame on the line then we must
         // be trying to place content where there's no room (e.g. on a
         // line with wide floats). Inform the caller to reflow the
         // line after skipping past a float.
@@ -4142,28 +4142,28 @@ nsBlockFrame::ReflowInlineFrame(BlockRef
         // was pushed, then mark the line as having word wrapped. We need to
         // know that if we're shrink wrapping our width
         if (pushedFrame) {
           aLine->SetLineWrapped(true);
         }
       }
     }
     else {
-      // If a float split and its prev-in-flow was followed by a <BR>, then combine 
-      // the <BR>'s break type with the inline's break type (the inline will be the very 
+      // If a float split and its prev-in-flow was followed by a <BR>, then combine
+      // the <BR>'s break type with the inline's break type (the inline will be the very
       // next frame after the split float).
-      if (NS_STYLE_CLEAR_NONE != aState.mFloatBreakType) {
+      if (StyleClear::None_ != aState.mFloatBreakType) {
         breakType = nsLayoutUtils::CombineBreakType(breakType,
                                                     aState.mFloatBreakType);
-        aState.mFloatBreakType = NS_STYLE_CLEAR_NONE;
+        aState.mFloatBreakType = StyleClear::None_;
       }
       // Break-after cases
-      if (breakType == NS_STYLE_CLEAR_LINE) {
+      if (breakType == StyleClear::Line) {
         if (!aLineLayout.GetLineEndsInBR()) {
-          breakType = NS_STYLE_CLEAR_NONE;
+          breakType = StyleClear::None_;
         }
       }
       aLine->SetBreakTypeAfter(breakType);
       if (NS_FRAME_IS_COMPLETE(frameReflowStatus)) {
         // Split line, but after the frame just reflowed
         SplitLine(aState, aLineLayout, aLine, aFrame->GetNextSibling(), aLineReflowStatus);
 
         if (NS_INLINE_IS_BREAK_AFTER(frameReflowStatus) &&
@@ -6221,29 +6221,29 @@ nsBlockFrame::ReflowFloat(BlockReflowInp
                     nsDidReflowStatus::FINISHED);
 
 #ifdef NOISY_FLOAT
   printf("end ReflowFloat %p, sized to %d,%d\n",
          aFloat, metrics.Width(), metrics.Height());
 #endif
 }
 
-uint8_t
+StyleClear
 nsBlockFrame::FindTrailingClear()
 {
   // find the break type of the last line
   for (nsIFrame* b = this; b; b = b->GetPrevInFlow()) {
     nsBlockFrame* block = static_cast<nsBlockFrame*>(b);
     line_iterator endLine = block->end_lines();
     if (endLine != block->begin_lines()) {
       --endLine;
       return endLine->GetBreakTypeAfter();
     }
   }
-  return NS_STYLE_CLEAR_NONE;
+  return StyleClear::None_;
 }
 
 void
 nsBlockFrame::ReflowPushedFloats(BlockReflowInput& aState,
                                  nsOverflowAreas&    aOverflowAreas,
                                  nsReflowStatus&     aStatus)
 {
   // Pushed floats live at the start of our float list; see comment
@@ -6302,17 +6302,17 @@ nsBlockFrame::ReflowPushedFloats(BlockRe
       // We didn't push |f| so its next-sibling is next.
       next = f->GetNextSibling();
       prev = f;
     } // else: we did push |f| so |prev|'s new next-sibling is next.
     f = next;
   }
 
   // If there are continued floats, then we may need to continue BR clearance
-  if (0 != aState.ClearFloats(0, NS_STYLE_CLEAR_BOTH)) {
+  if (0 != aState.ClearFloats(0, StyleClear::Both)) {
     nsBlockFrame* prevBlock = static_cast<nsBlockFrame*>(GetPrevInFlow());
     if (prevBlock) {
       aState.mFloatBreakType = prevBlock->FindTrailingClear();
     }
   }
 }
 
 void

--- a/layout/generic/nsBlockFrame.h
+++ b/layout/generic/nsBlockFrame.h
@@ -571,17 +571,17 @@ protected:
   /** Reflow pushed floats
    */
   void ReflowPushedFloats(BlockReflowInput& aState,
                           nsOverflowAreas&    aOverflowAreas,
                           nsReflowStatus&     aStatus);
 
   /** Find any trailing BR clear from the last line of the block (or its PIFs)
    */
-  uint8_t FindTrailingClear();
+  mozilla::StyleClear FindTrailingClear();
 
   /**
    * Remove a float from our float list.
    */
   void RemoveFloat(nsIFrame* aFloat);
   /**
    * Remove a float from the float cache for the line its placeholder is on.
    */

--- a/layout/generic/nsBlockReflowContext.cpp
+++ b/layout/generic/nsBlockReflowContext.cpp
@@ -163,17 +163,17 @@ nsBlockReflowContext::ComputeCollapsedBS
           {
             LogicalSize availSpace =
               outerReflowInput->ComputedSize(kid->GetWritingMode());
             ReflowInput innerReflowInput(prescontext,
                                                *outerReflowInput, kid,
                                                availSpace);
             // Record that we're being optimistic by assuming the kid
             // has no clearance
-            if (kid->StyleDisplay()->mBreakType != NS_STYLE_CLEAR_NONE ||
+            if (kid->StyleDisplay()->mBreakType != StyleClear::None_ ||
                 !nsBlockFrame::BlockCanIntersectFloats(kid)) {
               *aMayNeedRetry = true;
             }
             if (ComputeCollapsedBStartMargin(innerReflowInput, aMargin,
                                              aClearanceFrame, aMayNeedRetry,
                                              &isEmpty)) {
               line->MarkDirty();
               dirtiedLine = true;

--- a/layout/generic/nsFloatManager.cpp
+++ b/layout/generic/nsFloatManager.cpp
@@ -473,59 +473,59 @@ nsFloatManager::List(FILE* out) const
                    fi.LineLeft(), fi.BStart(), fi.ISize(), fi.BSize(),
                    fi.mLeftBEnd, fi.mRightBEnd);
   }
   return NS_OK;
 }
 #endif
 
 nscoord
-nsFloatManager::ClearFloats(nscoord aBCoord, uint8_t aBreakType,
+nsFloatManager::ClearFloats(nscoord aBCoord, StyleClear aBreakType,
                             uint32_t aFlags) const
 {
   if (!(aFlags & DONT_CLEAR_PUSHED_FLOATS) && ClearContinues(aBreakType)) {
     return nscoord_MAX;
   }
   if (!HasAnyFloats()) {
     return aBCoord;
   }
 
   nscoord blockEnd = aBCoord + mBlockStart;
 
   const FloatInfo &tail = mFloats[mFloats.Length() - 1];
   switch (aBreakType) {
-    case NS_STYLE_CLEAR_BOTH:
+    case StyleClear::Both:
       blockEnd = std::max(blockEnd, tail.mLeftBEnd);
       blockEnd = std::max(blockEnd, tail.mRightBEnd);
       break;
-    case NS_STYLE_CLEAR_LEFT:
+    case StyleClear::Left:
       blockEnd = std::max(blockEnd, tail.mLeftBEnd);
       break;
-    case NS_STYLE_CLEAR_RIGHT:
+    case StyleClear::Right:
       blockEnd = std::max(blockEnd, tail.mRightBEnd);
       break;
     default:
       // Do nothing
       break;
   }
 
   blockEnd -= mBlockStart;
 
   return blockEnd;
 }
 
 bool
-nsFloatManager::ClearContinues(uint8_t aBreakType) const
+nsFloatManager::ClearContinues(StyleClear aBreakType) const
 {
   return ((mPushedLeftFloatPastBreak || mSplitLeftFloatAcrossBreak) &&
-          (aBreakType == NS_STYLE_CLEAR_BOTH ||
-           aBreakType == NS_STYLE_CLEAR_LEFT)) ||
+          (aBreakType == StyleClear::Both ||
+           aBreakType == StyleClear::Left)) ||
          ((mPushedRightFloatPastBreak || mSplitRightFloatAcrossBreak) &&
-          (aBreakType == NS_STYLE_CLEAR_BOTH ||
-           aBreakType == NS_STYLE_CLEAR_RIGHT));
+          (aBreakType == StyleClear::Both ||
+           aBreakType == StyleClear::Right));
 }
 
 /////////////////////////////////////////////////////////////////////////////
 // FloatInfo
 
 nsFloatManager::FloatInfo::FloatInfo(nsIFrame* aFrame,
                                      nscoord aLineLeft, nscoord aBStart,
                                      nscoord aISize, nscoord aBSize)

--- a/layout/generic/nsFloatManager.h
+++ b/layout/generic/nsFloatManager.h
@@ -266,24 +266,24 @@ public:
    *
    * Both aBCoord and the result are relative to the current translation.
    */
   enum {
     // Tell ClearFloats not to push to nscoord_MAX when floats have been
     // pushed to the next page/column.
     DONT_CLEAR_PUSHED_FLOATS = (1<<0)
   };
-  nscoord ClearFloats(nscoord aBCoord, uint8_t aBreakType,
+  nscoord ClearFloats(nscoord aBCoord, mozilla::StyleClear aBreakType,
                       uint32_t aFlags = 0) const;
 
   /**
    * Checks if clear would pass into the floats' BFC's next-in-flow,
    * i.e. whether floats affecting this clear have continuations.
    */
-  bool ClearContinues(uint8_t aBreakType) const;
+  bool ClearContinues(mozilla::StyleClear aBreakType) const;
 
   void AssertStateMatches(SavedState *aState) const
   {
     NS_ASSERTION(aState->mLineLeft == mLineLeft &&
                  aState->mBlockStart == mBlockStart &&
                  aState->mPushedLeftFloatPastBreak ==
                    mPushedLeftFloatPastBreak &&
                  aState->mPushedRightFloatPastBreak ==

--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -4486,29 +4486,29 @@ nsIFrame::InlinePrefISizeData::ForceBrea
             // preferred widths accumulated for floats that have not yet
             // been cleared past
             floats_cur_left = 0,
             floats_cur_right = 0;
 
     for (uint32_t i = 0, i_end = mFloats.Length(); i != i_end; ++i) {
       const FloatInfo& floatInfo = mFloats[i];
       const nsStyleDisplay* floatDisp = floatInfo.Frame()->StyleDisplay();
-      uint8_t breakType = floatDisp->PhysicalBreakType(mLineContainerWM);
-      if (breakType == NS_STYLE_CLEAR_LEFT ||
-          breakType == NS_STYLE_CLEAR_RIGHT ||
-          breakType == NS_STYLE_CLEAR_BOTH) {
+      StyleClear breakType = floatDisp->PhysicalBreakType(mLineContainerWM);
+      if (breakType == StyleClear::Left ||
+          breakType == StyleClear::Right ||
+          breakType == StyleClear::Both) {
         nscoord floats_cur = NSCoordSaturatingAdd(floats_cur_left,
                                                   floats_cur_right);
         if (floats_cur > floats_done) {
           floats_done = floats_cur;
         }
-        if (breakType != NS_STYLE_CLEAR_RIGHT) {
+        if (breakType != StyleClear::Right) {
           floats_cur_left = 0;
         }
-        if (breakType != NS_STYLE_CLEAR_LEFT) {
+        if (breakType != StyleClear::Left) {
           floats_cur_right = 0;
         }
       }
 
       StyleFloat floatStyle = floatDisp->PhysicalFloats(mLineContainerWM);
       nscoord& floats_cur =
         floatStyle == StyleFloat::Left ? floats_cur_left : floats_cur_right;
       nscoord floatWidth = floatInfo.Width();

--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -280,35 +280,36 @@ typedef uint32_t nsReflowStatus;
   (0 != ((_status) & NS_INLINE_BREAK))
 
 #define NS_INLINE_IS_BREAK_AFTER(_status) \
   (0 != ((_status) & NS_INLINE_BREAK_AFTER))
 
 #define NS_INLINE_IS_BREAK_BEFORE(_status) \
   (NS_INLINE_BREAK == ((_status) & (NS_INLINE_BREAK|NS_INLINE_BREAK_AFTER)))
 
-#define NS_INLINE_GET_BREAK_TYPE(_status) (((_status) >> 12) & 0xF)
-
-#define NS_INLINE_MAKE_BREAK_TYPE(_type)  ((_type) << 12)
+#define NS_INLINE_GET_BREAK_TYPE(_status) \
+  (static_cast<StyleClear>(((_status) >> 12) & 0xF))
+
+#define NS_INLINE_MAKE_BREAK_TYPE(_type)  (static_cast<int>(_type) << 12)
 
 // Construct a line-break-before status. Note that there is no
 // completion status for a line-break before because we *know* that
 // the frame will be reflowed later and hence its current completion
 // status doesn't matter.
 #define NS_INLINE_LINE_BREAK_BEFORE()                                   \
   (NS_INLINE_BREAK | NS_INLINE_BREAK_BEFORE |                           \
-   NS_INLINE_MAKE_BREAK_TYPE(NS_STYLE_CLEAR_LINE))
+   NS_INLINE_MAKE_BREAK_TYPE(StyleClear::Line))
 
 // Take a completion status and add to it the desire to have a
 // line-break after. For this macro we do need the completion status
 // because the user of the status will need to know whether to
 // continue the frame or not.
 #define NS_INLINE_LINE_BREAK_AFTER(_completionStatus)                   \
   ((_completionStatus) | NS_INLINE_BREAK | NS_INLINE_BREAK_AFTER |      \
-   NS_INLINE_MAKE_BREAK_TYPE(NS_STYLE_CLEAR_LINE))
+   NS_INLINE_MAKE_BREAK_TYPE(StyleClear::Line))
 
 // A frame is "truncated" if the part of the frame before the first
 // possible break point was unable to fit in the available vertical
 // space.  Therefore, the entire frame should be moved to the next page.
 // A frame that begins at the top of the page must never be "truncated".
 // Doing so would likely cause an infinite loop.
 #define NS_FRAME_TRUNCATED  0x0010
 #define NS_FRAME_IS_TRUNCATED(status) \

--- a/layout/generic/nsLineBox.cpp
+++ b/layout/generic/nsLineBox.cpp
@@ -43,18 +43,17 @@ nsLineBox::nsLineBox(nsIFrame* aFrame, i
   ++ctorCount;
   NS_ASSERTION(!aIsBlock || aCount == 1, "Blocks must have exactly one child");
   nsIFrame* f = aFrame;
   for (int32_t n = aCount; n > 0; f = f->GetNextSibling(), --n) {
     NS_ASSERTION(aIsBlock == f->IsBlockOutside(),
                  "wrong kind of child frame");
   }
 #endif
-
-  static_assert(NS_STYLE_CLEAR_MAX <= 15,
+  static_assert(static_cast<int>(StyleClear::Max) <= 15,
                 "FlagBits needs more bits to store the full range of "
                 "break type ('clear') values");
   mChildCount = aCount;
   MarkDirty();
   mFlags.mBlock = aIsBlock;
 }
 
 nsLineBox::~nsLineBox()
@@ -188,26 +187,26 @@ ListFloats(FILE* out, const char* aPrefi
       str += "\n###!!! NULL out-of-flow frame";
     }
     fprintf_stderr(out, "%s\n", str.get());
     fc = fc->Next();
   }
 }
 
 const char*
-nsLineBox::BreakTypeToString(uint8_t aBreakType) const
+nsLineBox::BreakTypeToString(StyleClear aBreakType) const
 {
   switch (aBreakType) {
-    case NS_STYLE_CLEAR_NONE: return "nobr";
-    case NS_STYLE_CLEAR_LEFT: return "leftbr";
-    case NS_STYLE_CLEAR_RIGHT: return "rightbr";
-    case NS_STYLE_CLEAR_INLINE_START: return "inlinestartbr";
-    case NS_STYLE_CLEAR_INLINE_END: return "inlineendbr";
-    case NS_STYLE_CLEAR_BOTH: return "leftbr+rightbr";
-    case NS_STYLE_CLEAR_LINE: return "linebr";
+    case StyleClear::None_: return "nobr";
+    case StyleClear::Left: return "leftbr";
+    case StyleClear::Right: return "rightbr";
+    case StyleClear::InlineStart: return "inlinestartbr";
+    case StyleClear::InlineEnd: return "inlineendbr";
+    case StyleClear::Both: return "leftbr+rightbr";
+    case StyleClear::Line: return "linebr";
     default:
       break;
   }
   return "unknown";
 }
 
 char*
 nsLineBox::StateToString(char* aBuf, int32_t aBufSize) const

--- a/layout/generic/nsLineBox.h
+++ b/layout/generic/nsLineBox.h
@@ -138,17 +138,16 @@ public:
 protected:
   nsFloatCache* mTail;
 
   friend class nsFloatCacheList;
 };
 
 //----------------------------------------------------------------------
 
-#define LINE_MAX_BREAK_TYPE  ((1 << 4) - 1)
 #define LINE_MAX_CHILD_COUNT INT32_MAX
 
 /**
  * Function to create a line box and initialize it with a single frame.
  * The allocation is infallible.
  * If the frame was moved from another line then you're responsible
  * for notifying that line using NoteFrameRemoved().  Alternatively,
  * it's better to use the next function that does that for you in an
@@ -389,47 +388,48 @@ public:
       --mChildCount;
     }
   }
 
   // mBreakType value
   // Break information is applied *before* the line if the line is a block,
   // or *after* the line if the line is an inline. Confusing, I know, but
   // using different names should help.
+  using StyleClear = mozilla::StyleClear;
   bool HasBreakBefore() const {
-    return IsBlock() && NS_STYLE_CLEAR_NONE != mFlags.mBreakType;
+    return IsBlock() && StyleClear::None_ != BreakType();
   }
-  void SetBreakTypeBefore(uint8_t aBreakType) {
+  void SetBreakTypeBefore(StyleClear aBreakType) {
     NS_ASSERTION(IsBlock(), "Only blocks have break-before");
-    NS_ASSERTION(aBreakType == NS_STYLE_CLEAR_NONE ||
-                 aBreakType == NS_STYLE_CLEAR_LEFT ||
-                 aBreakType == NS_STYLE_CLEAR_RIGHT ||
-                 aBreakType == NS_STYLE_CLEAR_BOTH,
+    NS_ASSERTION(aBreakType == StyleClear::None_ ||
+                 aBreakType == StyleClear::Left ||
+                 aBreakType == StyleClear::Right ||
+                 aBreakType == StyleClear::Both,
                  "Only float break types are allowed before a line");
-    mFlags.mBreakType = aBreakType;
+    mFlags.mBreakType = static_cast<int>(aBreakType);
   }
-  uint8_t GetBreakTypeBefore() const {
-    return IsBlock() ? mFlags.mBreakType : NS_STYLE_CLEAR_NONE;
+  StyleClear GetBreakTypeBefore() const {
+    return IsBlock() ? BreakType() : StyleClear::None_;
   }
 
   bool HasBreakAfter() const {
-    return !IsBlock() && NS_STYLE_CLEAR_NONE != mFlags.mBreakType;
+    return !IsBlock() && StyleClear::None_ != BreakType();
   }
-  void SetBreakTypeAfter(uint8_t aBreakType) {
+  void SetBreakTypeAfter(StyleClear aBreakType) {
     NS_ASSERTION(!IsBlock(), "Only inlines have break-after");
-    NS_ASSERTION(aBreakType <= LINE_MAX_BREAK_TYPE, "bad break type");
-    mFlags.mBreakType = aBreakType;
+    mFlags.mBreakType = static_cast<int>(aBreakType);
   }
   bool HasFloatBreakAfter() const {
-    return !IsBlock() && (NS_STYLE_CLEAR_LEFT == mFlags.mBreakType ||
-                          NS_STYLE_CLEAR_RIGHT == mFlags.mBreakType ||
-                          NS_STYLE_CLEAR_BOTH == mFlags.mBreakType);
+    return !IsBlock() &&
+           (StyleClear::Left == BreakType() ||
+            StyleClear::Right == BreakType() ||
+            StyleClear::Both == BreakType());
   }
-  uint8_t GetBreakTypeAfter() const {
-    return !IsBlock() ? mFlags.mBreakType : NS_STYLE_CLEAR_NONE;
+  StyleClear GetBreakTypeAfter() const {
+    return !IsBlock() ? BreakType() : StyleClear::None_;
   }
 
   // mCarriedOutBEndMargin value
   nsCollapsingMargin GetCarriedOutBEndMargin() const;
   // Returns true if the margin changed
   bool SetCarriedOutBEndMargin(nsCollapsingMargin aValue);
 
   // mFloats
@@ -567,17 +567,17 @@ public:
   // list).
   static bool RFindLineContaining(nsIFrame* aFrame,
                                     const nsLineList_iterator& aBegin,
                                     nsLineList_iterator& aEnd,
                                     nsIFrame* aLastFrameBeforeEnd,
                                     int32_t* aFrameIndexInLine);
 
 #ifdef DEBUG_FRAME_DUMP
-  const char* BreakTypeToString(uint8_t aBreakType) const;
+  const char* BreakTypeToString(StyleClear aBreakType) const;
   char* StateToString(char* aBuf, int32_t aBufSize) const;
 
   void List(FILE* out, int32_t aIndent, uint32_t aFlags = 0) const;
   void List(FILE* out = stderr, const char* aPrefix = "", uint32_t aFlags = 0) const;
   nsIFrame* LastChild() const;
 #endif
 
 private:
@@ -659,17 +659,19 @@ public:
   struct FlagBits {
     uint32_t mDirty : 1;
     uint32_t mPreviousMarginDirty : 1;
     uint32_t mHasClearance : 1;
     uint32_t mBlock : 1;
     uint32_t mImpactedByFloat : 1;
     uint32_t mLineWrapped: 1;
     uint32_t mInvalidateTextRuns : 1;
-    uint32_t mResizeReflowOptimizationDisabled: 1;  // default 0 = means that the opt potentially applies to this line. 1 = never skip reflowing this line for a resize reflow
+    // default 0 = means that the opt potentially applies to this line.
+    // 1 = never skip reflowing this line for a resize reflow
+    uint32_t mResizeReflowOptimizationDisabled: 1;
     uint32_t mEmptyCacheValid: 1;
     uint32_t mEmptyCacheState: 1;
     // mHasBullet indicates that this is an inline line whose block's
     // bullet is adjacent to this line and non-empty.
     uint32_t mHasBullet : 1;
     // Indicates that this line *may* have a placeholder for a float
     // that was pushed to a later column or page.
     uint32_t mHadFloatPushed : 1;
@@ -695,21 +697,27 @@ public:
   struct ExtraInlineData : public ExtraData {
     explicit ExtraInlineData(const nsRect& aBounds) : ExtraData(aBounds) {
     }
     nsFloatCacheList mFloats;
   };
 
 protected:
   nscoord mAscent;           // see |SetAscent| / |GetAscent|
+  static_assert(sizeof(FlagBits) <= sizeof(uint32_t),
+                "size of FlagBits should not be larger than size of uint32_t");
   union {
     uint32_t mAllFlags;
     FlagBits mFlags;
   };
 
+  StyleClear BreakType() const {
+    return static_cast<StyleClear>(mFlags.mBreakType);
+  };
+
   union {
     ExtraData* mData;
     ExtraBlockData* mBlockData;
     ExtraInlineData* mInlineData;
   };
 
   void Cleanup();
   void MaybeFreeData();

--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -1053,23 +1053,23 @@ const KTableEntry nsCSSProps::kCaptionSi
   { eCSSKeyword_bottom,               NS_STYLE_CAPTION_SIDE_BOTTOM },
   { eCSSKeyword_left,                 NS_STYLE_CAPTION_SIDE_LEFT },
   { eCSSKeyword_top_outside,          NS_STYLE_CAPTION_SIDE_TOP_OUTSIDE },
   { eCSSKeyword_bottom_outside,       NS_STYLE_CAPTION_SIDE_BOTTOM_OUTSIDE },
   { eCSSKeyword_UNKNOWN,              -1 }
 };
 
 KTableEntry nsCSSProps::kClearKTable[] = {
-  { eCSSKeyword_none,         NS_STYLE_CLEAR_NONE },
-  { eCSSKeyword_left,         NS_STYLE_CLEAR_LEFT },
-  { eCSSKeyword_right,        NS_STYLE_CLEAR_RIGHT },
-  { eCSSKeyword_inline_start, NS_STYLE_CLEAR_INLINE_START },
-  { eCSSKeyword_inline_end,   NS_STYLE_CLEAR_INLINE_END },
-  { eCSSKeyword_both,         NS_STYLE_CLEAR_BOTH },
-  { eCSSKeyword_UNKNOWN,      -1 }
+  { eCSSKeyword_none, StyleClear::None_ },
+  { eCSSKeyword_left, StyleClear::Left },
+  { eCSSKeyword_right, StyleClear::Right },
+  { eCSSKeyword_inline_start, StyleClear::InlineStart },
+  { eCSSKeyword_inline_end, StyleClear::InlineEnd },
+  { eCSSKeyword_both, StyleClear::Both },
+  { eCSSKeyword_UNKNOWN, -1 }
 };
 
 // See also kContextPatternKTable for SVG paint-specific values
 const KTableEntry nsCSSProps::kColorKTable[] = {
   { eCSSKeyword_activeborder, LookAndFeel::eColorID_activeborder },
   { eCSSKeyword_activecaption, LookAndFeel::eColorID_activecaption },
   { eCSSKeyword_appworkspace, LookAndFeel::eColorID_appworkspace },
   { eCSSKeyword_background, LookAndFeel::eColorID_background },

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -1337,16 +1337,17 @@ struct SetEnumValueHelper
   }
 
   DEFINE_ENUM_CLASS_SETTER(StyleBoxAlign, Stretch, End)
   DEFINE_ENUM_CLASS_SETTER(StyleBoxDecorationBreak, Slice, Clone)
   DEFINE_ENUM_CLASS_SETTER(StyleBoxDirection, Normal, Reverse)
   DEFINE_ENUM_CLASS_SETTER(StyleBoxOrient, Horizontal, Vertical)
   DEFINE_ENUM_CLASS_SETTER(StyleBoxPack, Start, Justify)
   DEFINE_ENUM_CLASS_SETTER(StyleBoxSizing, Content, Border)
+  DEFINE_ENUM_CLASS_SETTER(StyleClear, None_, Both)
   DEFINE_ENUM_CLASS_SETTER(StyleFillRule, Nonzero, Evenodd)
   DEFINE_ENUM_CLASS_SETTER(StyleFloat, None_, InlineEnd)
   DEFINE_ENUM_CLASS_SETTER(StyleFloatEdge, ContentBox, MarginBox)
   DEFINE_ENUM_CLASS_SETTER(StyleUserFocus, None_, SelectMenu)
   DEFINE_ENUM_CLASS_SETTER(StyleUserSelect, None_, MozText)
 #ifdef MOZ_XUL
   DEFINE_ENUM_CLASS_SETTER(StyleDisplay, None_, Popup)
 #else
@@ -6039,17 +6040,17 @@ nsRuleNode::ComputeDisplayData(void* aSt
     // an aStartStruct for some other elements.
     conditions.SetUncacheable();
   }
 
   // clear: enum, inherit, initial
   SetValue(*aRuleData->ValueForClear(), display->mBreakType, conditions,
            SETVAL_ENUMERATED | SETVAL_UNSET_INITIAL,
            parentDisplay->mBreakType,
-           NS_STYLE_CLEAR_NONE);
+           StyleClear::None_);
 
   // temp fix for bug 24000
   // Map 'auto' and 'avoid' to false, and 'always', 'left', and
   // 'right' to true.
   // "A conforming user agent may interpret the values 'left' and
   // 'right' as 'always'." - CSS2.1, section 13.3.1
   const nsCSSValue* breakBeforeValue = aRuleData->ValueForPageBreakBefore();
   if (eCSSUnit_Enumerated == breakBeforeValue->GetUnit()) {

--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -103,16 +103,30 @@ enum class StyleBoxSizing : uint8_t {
   Border
 };
 
 // box-shadow
 enum class StyleBoxShadowType : uint8_t {
   Inset,
 };
 
+// clear
+enum class StyleClear : uint8_t {
+  None_ = 0,
+  Left,
+  Right,
+  InlineStart,
+  InlineEnd,
+  Both,
+  // StyleClear::Line can be added to one of the other values in layout
+  // so it needs to use a bit value that none of the other values can have.
+  Line = 8,
+  Max = 13  // Max = (Both | Line)
+};
+
 // clip-path geometry box
 enum class StyleClipPathGeometryBox : uint8_t {
   NoBox,
   Content,
   Padding,
   Border,
   Margin,
   Fill,
@@ -398,28 +412,16 @@ enum class FillMode : uint32_t;
 #define NS_STYLE_BORDER_IMAGE_REPEAT_STRETCH    0
 #define NS_STYLE_BORDER_IMAGE_REPEAT_REPEAT     1
 #define NS_STYLE_BORDER_IMAGE_REPEAT_ROUND      2
 #define NS_STYLE_BORDER_IMAGE_REPEAT_SPACE      3
 
 #define NS_STYLE_BORDER_IMAGE_SLICE_NOFILL      0
 #define NS_STYLE_BORDER_IMAGE_SLICE_FILL        1
 
-// See nsStyleDisplay
-#define NS_STYLE_CLEAR_NONE                     0
-#define NS_STYLE_CLEAR_LEFT                     1
-#define NS_STYLE_CLEAR_RIGHT                    2
-#define NS_STYLE_CLEAR_INLINE_START             3
-#define NS_STYLE_CLEAR_INLINE_END               4
-#define NS_STYLE_CLEAR_BOTH                     5
-#define NS_STYLE_CLEAR_LINE                     8
-// @note NS_STYLE_CLEAR_LINE can be added to one of the other values in layout
-// so it needs to use a bit value that none of the other values can have.
-#define NS_STYLE_CLEAR_MAX (NS_STYLE_CLEAR_LINE | NS_STYLE_CLEAR_BOTH)
-
 // See nsStyleContent
 #define NS_STYLE_CONTENT_OPEN_QUOTE             0
 #define NS_STYLE_CONTENT_CLOSE_QUOTE            1
 #define NS_STYLE_CONTENT_NO_OPEN_QUOTE          2
 #define NS_STYLE_CONTENT_NO_CLOSE_QUOTE         3
 #define NS_STYLE_CONTENT_ALT_CONTENT            4
 
 // See nsStyleColor

--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -2983,17 +2983,17 @@ StyleAnimation::operator==(const StyleAn
 nsStyleDisplay::nsStyleDisplay(StyleStructContext aContext)
   : mDisplay(StyleDisplay::Inline)
   , mOriginalDisplay(StyleDisplay::Inline)
   , mContain(NS_STYLE_CONTAIN_NONE)
   , mAppearance(NS_THEME_NONE)
   , mPosition(NS_STYLE_POSITION_STATIC)
   , mFloat(StyleFloat::None_)
   , mOriginalFloat(StyleFloat::None_)
-  , mBreakType(NS_STYLE_CLEAR_NONE)
+  , mBreakType(StyleClear::None_)
   , mBreakInside(NS_STYLE_PAGE_BREAK_AUTO)
   , mBreakBefore(false)
   , mBreakAfter(false)
   , mOverflowX(NS_STYLE_OVERFLOW_VISIBLE)
   , mOverflowY(NS_STYLE_OVERFLOW_VISIBLE)
   , mOverflowClipBox(NS_STYLE_OVERFLOW_CLIP_BOX_PADDING_BOX)
   , mResize(NS_STYLE_RESIZE_NONE)
   , mOrient(NS_STYLE_ORIENT_INLINE)

--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -2835,17 +2835,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
   uint8_t mAppearance;          // [reset]
   uint8_t mPosition;            // [reset] see nsStyleConsts.h
 
   // [reset] See StyleFloat in nsStyleConsts.h.
   mozilla::StyleFloat mFloat;
   // [reset] Save mFloat for position:absolute/fixed; otherwise equal to mFloat.
   mozilla::StyleFloat mOriginalFloat;
 
-  uint8_t mBreakType;           // [reset] see nsStyleConsts.h NS_STYLE_CLEAR_*
+  mozilla::StyleClear mBreakType;  // [reset]
   uint8_t mBreakInside;         // [reset] NS_STYLE_PAGE_BREAK_AUTO/AVOID
   bool mBreakBefore;    // [reset]
   bool mBreakAfter;     // [reset]
   uint8_t mOverflowX;           // [reset] see nsStyleConsts.h
   uint8_t mOverflowY;           // [reset] see nsStyleConsts.h
   uint8_t mOverflowClipBox;     // [reset] see nsStyleConsts.h
   uint8_t mResize;              // [reset] see nsStyleConsts.h
   uint8_t mOrient;              // [reset] see nsStyleConsts.h
@@ -3089,17 +3089,17 @@ private:
   inline bool HasFixedPosContainingBlockStyleInternal(
                 StyleContextLike* aStyleContext) const;
 
 public:
   // Return the 'float' and 'clear' properties, with inline-{start,end} values
   // resolved to {left,right} according to the given writing mode. These are
   // defined in WritingModes.h.
   inline mozilla::StyleFloat PhysicalFloats(mozilla::WritingMode aWM) const;
-  inline uint8_t PhysicalBreakType(mozilla::WritingMode aWM) const;
+  inline mozilla::StyleClear PhysicalBreakType(mozilla::WritingMode aWM) const;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleTable
 {
   explicit nsStyleTable(StyleStructContext aContext);
   nsStyleTable(const nsStyleTable& aOther);
   ~nsStyleTable();