@@ -1420,7 +1420,19 @@ nsRefreshDriver::nsRefreshDriver(nsPresContext* aPresContext)
       mFreezeCount(0),
       mThrottledFrameRequestInterval(
           TimeDuration::FromMilliseconds(GetThrottledTimerInterval())),
-      mMinRecomputeVisibilityInterval(GetMinRecomputeVisibilityInterval()) {
+      mMinRecomputeVisibilityInterval(GetMinRecomputeVisibilityInterval()),
+      mThrottled(false),
+      mNeedToRecomputeVisibility(false),
+      mTestControllingRefreshes(false),
+      mInRefresh(false),
+      mWaitingForTransaction(false),
+      mSkippedPaints(false),
+      mResizeSuppressed(false),
+      mInNormalTick(false),
+      mAttemptedExtraTickSinceLastVsync(false),
+      mHasExceededAfterLoadTickPeriod(false),
+      mHasImageAnimations(false),
+      mHasStartedTimerAtLeastOnce(false) {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(mPresContext,
              "Need a pres context to tell us to call Disconnect() later "
 
@@ -502,40 +502,40 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
 
   mozilla::UniquePtr<mozilla::ProfileChunkedBuffer> mPaintCause;
 
-  bool mThrottled : 1 = false;
-  bool mNeedToRecomputeVisibility : 1 = false;
-  bool mTestControllingRefreshes : 1 = false;
-  bool mInRefresh : 1 = false;
+  bool mThrottled : 1;
+  bool mNeedToRecomputeVisibility : 1;
+  bool mTestControllingRefreshes : 1;
+  bool mInRefresh : 1;
 
   // True if the refresh driver is suspended waiting for transaction
   // id's to be returned and shouldn't do any work during Tick().
-  bool mWaitingForTransaction : 1 = false;
+  bool mWaitingForTransaction : 1;
   // True if Tick() was skipped because of mWaitingForTransaction and
   // we should schedule a new Tick immediately when resumed instead
   // of waiting until the next interval.
-  bool mSkippedPaints : 1 = false;
+  bool mSkippedPaints : 1;
 
   // True if view managers should delay any resize request until the
   // next tick by the refresh driver. This flag will be reset at the
   // start of every tick.
-  bool mResizeSuppressed : 1 = false;
+  bool mResizeSuppressed : 1;
 
   // True if we may need to run any frame callback.
-  bool mNeedToRunFrameRequestCallbacks : 1 = false;
+  bool mNeedToRunFrameRequestCallbacks : 1;
 
   // True if we're currently within the scope of Tick() handling a normal
   // (timer-driven) tick.
-  bool mInNormalTick : 1 = false;
+  bool mInNormalTick : 1;
 
   // True if we attempted an extra tick (see CanDoExtraTick) since the last
   // vsync and thus shouldn't allow another.
-  bool mAttemptedExtraTickSinceLastVsync : 1 = false;
+  bool mAttemptedExtraTickSinceLastVsync : 1;
 
-  bool mHasExceededAfterLoadTickPeriod : 1 = false;
+  bool mHasExceededAfterLoadTickPeriod : 1;
 
-  bool mHasImageAnimations : 1 = false;
+  bool mHasImageAnimations : 1;
 
-  bool mHasStartedTimerAtLeastOnce : 1 = false;
+  bool mHasStartedTimerAtLeastOnce : 1;
 
   mozilla::TimeStamp mMostRecentRefresh;
   mozilla::TimeStamp mTickStart;
 
@@ -84,7 +84,7 @@ class nsFirstLetterFrame : public nsContainerFrame {
   bool UseTightBounds() const;
 
  protected:
-  nscoord mBaseline = 0;
+  nscoord mBaseline;
 
   void DrainOverflowFrames(nsPresContext* aPresContext);
 };
 
@@ -187,8 +187,8 @@ class nsHTMLFramesetFrame final : public nsContainerFrame {
   bool mNeedFirstReflowWork = false;
   nscolor mParentBorderColor;
   int32_t mParentBorderWidth;
-  int32_t mPrevNeighborOrigSize = 0;  // used during resize
-  int32_t mNextNeighborOrigSize = 0;
+  int32_t mPrevNeighborOrigSize;  // used during resize
+  int32_t mNextNeighborOrigSize;
   int32_t mMinDrag;
   int32_t mChildCount;
 };
 
@@ -87,7 +87,7 @@ class nsRubyBaseContainerFrame final : public nsContainerFrame {
   void PullOneColumn(nsLineLayout* aLineLayout, PullFrameState& aPullFrameState,
                      mozilla::RubyColumn& aColumn, bool& aIsComplete);
 
-  nscoord mBaseline = 0;
+  nscoord mBaseline;
 
   // Leading produced by descendant ruby annotations.
   mozilla::RubyBlockLeadings mDescendantLeadings;
 
@@ -59,7 +59,7 @@ class RemoteLayerTreeOwner final {
  private:
   // The process id of the remote frame. This is used by the compositor to
   // do security checks on incoming layer transactions.
-  base::ProcessId mTabProcessId = 0;
+  base::ProcessId mTabProcessId;
   // The layers id of the remote frame.
   LayersId mLayersId;
   // The compositor options for this layers id. This is only meaningful if
 
@@ -1197,7 +1197,7 @@ class nsMathMLContainerFrame::RowChildFrameIterator {
   bool mAddOperatorSpacing;
   nsMargin mMargin;
 
-  nscoord mItalicCorrection = 0;
+  nscoord mItalicCorrection;
   MathMLFrameType mChildFrameType;
   int32_t mCarrySpace;
   MathMLFrameType mFromFrameType;
 
@@ -3742,10 +3742,7 @@ bool nsDisplayTableBackgroundImage::IsInvalid(nsRect& aRect) const {
 nsDisplayThemedBackground::nsDisplayThemedBackground(
     nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
     const nsRect& aBackgroundRect)
-    : nsPaintedDisplayItem(aBuilder, aFrame),
-      mBackgroundRect(aBackgroundRect),
-      mThemeTransparency(nsITheme::eUnknownTransparency),
-      mAppearance(StyleAppearance::None) {
+    : nsPaintedDisplayItem(aBuilder, aFrame), mBackgroundRect(aBackgroundRect) {
   MOZ_COUNT_CTOR(nsDisplayThemedBackground);
 }
 
 
@@ -172,7 +172,7 @@ class nsDisplaySVGEffectGeometry : public nsDisplayItemGeometry {
   gfxRect mBBox;
   gfxPoint mUserSpaceOffset;
   nsPoint mFrameOffsetToReferenceFrame;
-  bool mHandleOpacity = false;
+  bool mHandleOpacity;
 };
 
 class nsDisplayMasksAndClipPathsGeometry : public nsDisplaySVGEffectGeometry {
 
@@ -245,7 +245,7 @@ class SVGFilterInstance {
   /**
    * The 'primitiveUnits' attribute value (objectBoundingBox or userSpaceOnUse).
    */
-  uint16_t mPrimitiveUnits = SVG_UNIT_TYPE_USERSPACEONUSE;
+  uint16_t mPrimitiveUnits;
 
   /**
    * The index of the FilterPrimitiveDescription that this SVG filter should use