diff --git a/layout/forms/nsDateTimeControlFrame.cpp b/layout/forms/nsDateTimeControlFrame.cpp
index 11b2995d64f9..7a2e31b57389 100644
--- a/layout/forms/nsDateTimeControlFrame.cpp
+++ b/layout/forms/nsDateTimeControlFrame.cpp
@@ -404,7 +404,7 @@ nsDateTimeControlFrame::AttributeChanged(int32_t aNameSpaceID,
         aAttribute == nsGkAtoms::readonly ||
         aAttribute == nsGkAtoms::tabindex) {
       MOZ_ASSERT(mContent->IsHTMLElement(nsGkAtoms::input), "bad cast");
-      auto contentAsInputElem = static_cast<dom::HTMLInputElement*>(mContent);
+      auto contentAsInputElem = static_cast<dom::HTMLInputElement*>(GetContent());
       // If script changed the <input>'s type before setting these attributes
       // then we don't need to do anything since we are going to be reframed.
       if (contentAsInputElem->ControlType() == NS_FORM_INPUT_TIME ||
diff --git a/layout/forms/nsMeterFrame.cpp b/layout/forms/nsMeterFrame.cpp
index d007c016474c..58e2ba559fd7 100644
--- a/layout/forms/nsMeterFrame.cpp
+++ b/layout/forms/nsMeterFrame.cpp
@@ -145,7 +145,7 @@ nsMeterFrame::ReflowBarFrame(nsIFrame*                aBarFrame,
   nscoord yoffset = aReflowInput.ComputedPhysicalBorderPadding().top;
 
   // NOTE: Introduce a new function getPosition in the content part ?
-  HTMLMeterElement* meterElement = static_cast<HTMLMeterElement*>(mContent);
+  HTMLMeterElement* meterElement = static_cast<HTMLMeterElement*>(GetContent());
 
   double max = meterElement->Max();
   double min = meterElement->Min();
diff --git a/layout/forms/nsProgressFrame.cpp b/layout/forms/nsProgressFrame.cpp
index fcc8cf46e094..40f564fe9ed6 100644
--- a/layout/forms/nsProgressFrame.cpp
+++ b/layout/forms/nsProgressFrame.cpp
@@ -151,7 +151,7 @@ nsProgressFrame::ReflowChildFrame(nsIFrame*          aChild,
   nscoord xoffset = aReflowInput.ComputedPhysicalBorderPadding().left;
   nscoord yoffset = aReflowInput.ComputedPhysicalBorderPadding().top;
 
-  double position = static_cast<HTMLProgressElement*>(mContent)->Position();
+  double position = static_cast<HTMLProgressElement*>(GetContent())->Position();
 
   // Force the bar's size to match the current progress.
   // When indeterminate, the progress' size will be 100%.
diff --git a/layout/forms/nsRangeFrame.cpp b/layout/forms/nsRangeFrame.cpp
index c672517b7cca..93f7517db8e7 100644
--- a/layout/forms/nsRangeFrame.cpp
+++ b/layout/forms/nsRangeFrame.cpp
@@ -486,7 +486,7 @@ double
 nsRangeFrame::GetValueAsFractionOfRange()
 {
   MOZ_ASSERT(mContent->IsHTMLElement(nsGkAtoms::input), "bad cast");
-  dom::HTMLInputElement* input = static_cast<dom::HTMLInputElement*>(mContent);
+  dom::HTMLInputElement* input = static_cast<dom::HTMLInputElement*>(GetContent());
 
   MOZ_ASSERT(input->ControlType() == NS_FORM_INPUT_RANGE);
 
@@ -515,7 +515,7 @@ nsRangeFrame::GetValueAtEventPoint(WidgetGUIEvent* aEvent)
              "Unexpected event type - aEvent->mRefPoint may be meaningless");
 
   MOZ_ASSERT(mContent->IsHTMLElement(nsGkAtoms::input), "bad cast");
-  dom::HTMLInputElement* input = static_cast<dom::HTMLInputElement*>(mContent);
+  dom::HTMLInputElement* input = static_cast<dom::HTMLInputElement*>(GetContent());
 
   MOZ_ASSERT(input->ControlType() == NS_FORM_INPUT_RANGE);
 
@@ -541,7 +541,7 @@ nsRangeFrame::GetValueAtEventPoint(WidgetGUIEvent* aEvent)
 
   if (point == nsPoint(NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE)) {
     // We don't want to change the current value for this error state.
-    return static_cast<dom::HTMLInputElement*>(mContent)->GetValueAsDecimal();
+    return static_cast<dom::HTMLInputElement*>(GetContent())->GetValueAsDecimal();
   }
 
   nsRect rangeContentRect = GetContentRectRelativeToSelf();
@@ -750,7 +750,7 @@ nsRangeFrame::AttributeChanged(int32_t  aNameSpaceID,
       // UpdateForValueChange() anyway.
       MOZ_ASSERT(mContent->IsHTMLElement(nsGkAtoms::input), "bad cast");
       bool typeIsRange =
-        static_cast<dom::HTMLInputElement*>(mContent)->ControlType() ==
+        static_cast<dom::HTMLInputElement*>(GetContent())->ControlType() ==
                            NS_FORM_INPUT_RANGE;
       // If script changed the <input>'s type before setting these attributes
       // then we don't need to do anything since we are going to be reframed.
@@ -837,7 +837,7 @@ bool
 nsRangeFrame::IsHorizontal() const
 {
   dom::HTMLInputElement* element =
-    static_cast<dom::HTMLInputElement*>(mContent);
+    static_cast<dom::HTMLInputElement*>(GetContent());
   return element->AttrValueIs(kNameSpaceID_None, nsGkAtoms::orient,
                               nsGkAtoms::horizontal, eCaseMatters) ||
          (!element->AttrValueIs(kNameSpaceID_None, nsGkAtoms::orient,
@@ -850,19 +850,19 @@ nsRangeFrame::IsHorizontal() const
 double
 nsRangeFrame::GetMin() const
 {
-  return static_cast<dom::HTMLInputElement*>(mContent)->GetMinimum().toDouble();
+  return static_cast<dom::HTMLInputElement*>(GetContent())->GetMinimum().toDouble();
 }
 
 double
 nsRangeFrame::GetMax() const
 {
-  return static_cast<dom::HTMLInputElement*>(mContent)->GetMaximum().toDouble();
+  return static_cast<dom::HTMLInputElement*>(GetContent())->GetMaximum().toDouble();
 }
 
 double
 nsRangeFrame::GetValue() const
 {
-  return static_cast<dom::HTMLInputElement*>(mContent)->GetValueAsDecimal().toDouble();
+  return static_cast<dom::HTMLInputElement*>(GetContent())->GetValueAsDecimal().toDouble();
 }
 
 #define STYLES_DISABLING_NATIVE_THEMING \
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 109607f488ea..cb639bf76ffb 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -3323,7 +3323,7 @@ nsFrame::GetContentForEvent(WidgetEvent* aEvent,
 void
 nsFrame::FireDOMEvent(const nsAString& aDOMEventName, nsIContent *aContent)
 {
-  nsIContent* target = aContent ? aContent : mContent;
+  nsIContent* target = aContent ? aContent : GetContent();
 
   if (target) {
     RefPtr<AsyncEventDispatcher> asyncDispatcher =
diff --git a/layout/svg/SVGFEContainerFrame.cpp b/layout/svg/SVGFEContainerFrame.cpp
index d6f31428d985..ae4a94edbfbc 100644
--- a/layout/svg/SVGFEContainerFrame.cpp
+++ b/layout/svg/SVGFEContainerFrame.cpp
@@ -85,7 +85,7 @@ SVGFEContainerFrame::AttributeChanged(int32_t  aNameSpaceID,
                                       nsIAtom* aAttribute,
                                       int32_t  aModType)
 {
-  nsSVGFE *element = static_cast<nsSVGFE*>(mContent);
+  nsSVGFE *element = static_cast<nsSVGFE*>(GetContent());
   if (element->AttributeAffectsRendering(aNameSpaceID, aAttribute)) {
     MOZ_ASSERT(GetParent()->IsSVGFilterFrame(),
                "Observers observe the filter, so that's what we must invalidate");
diff --git a/layout/svg/SVGFEImageFrame.cpp b/layout/svg/SVGFEImageFrame.cpp
index a6d0c9d587c4..d5dd7b623e4d 100644
--- a/layout/svg/SVGFEImageFrame.cpp
+++ b/layout/svg/SVGFEImageFrame.cpp
@@ -121,7 +121,7 @@ SVGFEImageFrame::AttributeChanged(int32_t  aNameSpaceID,
                                   nsIAtom* aAttribute,
                                   int32_t  aModType)
 {
-  SVGFEImageElement* element = static_cast<SVGFEImageElement*>(mContent);
+  SVGFEImageElement* element = static_cast<SVGFEImageElement*>(GetContent());
   if (element->AttributeAffectsRendering(aNameSpaceID, aAttribute)) {
     MOZ_ASSERT(GetParent()->IsSVGFilterFrame(),
                "Observers observe the filter, so that's what we must invalidate");
diff --git a/layout/svg/SVGFELeafFrame.cpp b/layout/svg/SVGFELeafFrame.cpp
index 71a1bb1a16e8..b72c0cc00981 100644
--- a/layout/svg/SVGFELeafFrame.cpp
+++ b/layout/svg/SVGFELeafFrame.cpp
@@ -83,7 +83,7 @@ SVGFELeafFrame::AttributeChanged(int32_t  aNameSpaceID,
                                  nsIAtom* aAttribute,
                                  int32_t  aModType)
 {
-  nsSVGFE *element = static_cast<nsSVGFE*>(mContent);
+  nsSVGFE *element = static_cast<nsSVGFE*>(GetContent());
   if (element->AttributeAffectsRendering(aNameSpaceID, aAttribute)) {
     MOZ_ASSERT(GetParent()->IsSVGFilterFrame(),
                "Observers observe the filter, so that's what we must invalidate");
diff --git a/layout/svg/SVGFEUnstyledLeafFrame.cpp b/layout/svg/SVGFEUnstyledLeafFrame.cpp
index 41fa61b7b82b..8b6548765019 100644
--- a/layout/svg/SVGFEUnstyledLeafFrame.cpp
+++ b/layout/svg/SVGFEUnstyledLeafFrame.cpp
@@ -62,7 +62,7 @@ SVGFEUnstyledLeafFrame::AttributeChanged(int32_t  aNameSpaceID,
                                          nsIAtom* aAttribute,
                                          int32_t  aModType)
 {
-  SVGFEUnstyledElement *element = static_cast<SVGFEUnstyledElement*>(mContent);
+  SVGFEUnstyledElement *element = static_cast<SVGFEUnstyledElement*>(GetContent());
   if (element->AttributeAffectsRendering(aNameSpaceID, aAttribute)) {
     MOZ_ASSERT(GetParent()->GetParent()->IsSVGFilterFrame(),
                "Observers observe the filter, so that's what we must invalidate");
diff --git a/layout/svg/SVGGeometryFrame.cpp b/layout/svg/SVGGeometryFrame.cpp
index 7a3439d21341..c3b625620e13 100644
--- a/layout/svg/SVGGeometryFrame.cpp
+++ b/layout/svg/SVGGeometryFrame.cpp
@@ -177,7 +177,7 @@ SVGGeometryFrame::AttributeChanged(int32_t         aNameSpaceID,
 
   if (aNameSpaceID == kNameSpaceID_None &&
       (static_cast<SVGGeometryElement*>
-                  (mContent)->AttributeDefinesGeometry(aAttribute))) {
+                  (GetContent())->AttributeDefinesGeometry(aAttribute))) {
     nsLayoutUtils::PostRestyleEvent(
       mContent->AsElement(), nsRestyleHint(0),
       nsChangeHint_InvalidateRenderingObservers);
@@ -202,10 +202,10 @@ SVGGeometryFrame::DidSetStyleContext(nsStyleContext* aOldStyleContext)
     }
 
     SVGGeometryElement* element =
-      static_cast<SVGGeometryElement*>(mContent);
+      static_cast<SVGGeometryElement*>(GetContent());
 
     auto oldStyleSVG = aOldStyleContext->PeekStyleSVG();
-    if (oldStyleSVG && !SVGContentUtils::ShapeTypeHasNoCorners(mContent)) {
+    if (oldStyleSVG && !SVGContentUtils::ShapeTypeHasNoCorners(GetContent())) {
       if (StyleSVG()->mStrokeLinecap != oldStyleSVG->mStrokeLinecap &&
           element->IsSVGElement(nsGkAtoms::path)) {
         // If the stroke-linecap changes to or from "butt" then our element
@@ -243,7 +243,7 @@ SVGGeometryFrame::IsSVGTransformed(gfx::Matrix *aOwnTransform,
                        HasChildrenOnlyTransform(aFromParentTransform);
   }
 
-  nsSVGElement *content = static_cast<nsSVGElement*>(mContent);
+  nsSVGElement *content = static_cast<nsSVGElement*>(GetContent());
   nsSVGAnimatedTransformList* transformList =
     content->GetAnimatedTransformList();
   if ((transformList && transformList->HasTransform()) ||
@@ -263,7 +263,7 @@ void
 SVGGeometryFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                    const nsDisplayListSet& aLists)
 {
-  if (!static_cast<const nsSVGElement*>(mContent)->HasValidDimensions() ||
+  if (!static_cast<const nsSVGElement*>(GetContent())->HasValidDimensions() ||
       (!IsVisibleForPainting(aBuilder) && aBuilder->IsForPainting())) {
     return;
   }
@@ -342,7 +342,7 @@ SVGGeometryFrame::GetFrameForPoint(const gfxPoint& aPoint)
   bool isHit = false;
 
   SVGGeometryElement* content =
-    static_cast<SVGGeometryElement*>(mContent);
+    static_cast<SVGGeometryElement*>(GetContent());
 
   // Using ScreenReferenceDrawTarget() opens us to Moz2D backend specific hit-
   // testing bugs. Maybe we should use a BackendType::CAIRO DT for hit-testing
@@ -460,9 +460,9 @@ SVGGeometryFrame::NotifySVGChanged(uint32_t aFlags)
     // of stroke-dashoffset since, although that can have a percentage value
     // that is resolved against our coordinate context, it does not affect our
     // mRect.
-    if (static_cast<SVGGeometryElement*>(mContent)->GeometryDependsOnCoordCtx() ||
+    if (static_cast<SVGGeometryElement*>(GetContent())->GeometryDependsOnCoordCtx() ||
         StyleSVG()->mStrokeWidth.HasPercent()) {
-      static_cast<SVGGeometryElement*>(mContent)->ClearAnyCachedPath();
+      static_cast<SVGGeometryElement*>(GetContent())->ClearAnyCachedPath();
       nsSVGUtils::ScheduleReflowSVG(this);
     }
   }
@@ -493,7 +493,7 @@ SVGGeometryFrame::GetBBoxContribution(const Matrix &aToBBoxUserspace,
   }
 
   SVGGeometryElement* element =
-    static_cast<SVGGeometryElement*>(mContent);
+    static_cast<SVGGeometryElement*>(GetContent());
 
   bool getFill = (aFlags & nsSVGUtils::eBBoxIncludeFillGeometry) ||
                  ((aFlags & nsSVGUtils::eBBoxIncludeFill) &&
@@ -646,14 +646,14 @@ SVGGeometryFrame::GetBBoxContribution(const Matrix &aToBBoxUserspace,
 
   // Account for markers:
   if ((aFlags & nsSVGUtils::eBBoxIncludeMarkers) != 0 &&
-      static_cast<SVGGeometryElement*>(mContent)->IsMarkable()) {
+      static_cast<SVGGeometryElement*>(GetContent())->IsMarkable()) {
 
     float strokeWidth = nsSVGUtils::GetStrokeWidth(this);
     MarkerProperties properties = GetMarkerProperties(this);
 
     if (properties.MarkersExist()) {
       nsTArray<nsSVGMark> marks;
-      static_cast<SVGGeometryElement*>(mContent)->GetMarkPoints(&marks);
+      static_cast<SVGGeometryElement*>(GetContent())->GetMarkPoints(&marks);
       uint32_t num = marks.Length();
 
       // These are in the same order as the nsSVGMark::Type constants.
@@ -691,7 +691,7 @@ SVGGeometryFrame::GetCanvasTM()
   NS_ASSERTION(GetParent(), "null parent");
 
   nsSVGContainerFrame *parent = static_cast<nsSVGContainerFrame*>(GetParent());
-  SVGGraphicsElement *content = static_cast<SVGGraphicsElement*>(mContent);
+  SVGGraphicsElement *content = static_cast<SVGGraphicsElement*>(GetContent());
 
   return content->PrependLocalTransformsTo(parent->GetCanvasTM());
 }
@@ -762,7 +762,7 @@ SVGGeometryFrame::Render(gfxContext* aContext,
                              StyleSVG()->mClipRule : StyleSVG()->mFillRule);
 
   SVGGeometryElement* element =
-    static_cast<SVGGeometryElement*>(mContent);
+    static_cast<SVGGeometryElement*>(GetContent());
 
   AntialiasMode aaMode =
     (StyleSVG()->mShapeRendering == NS_STYLE_SHAPE_RENDERING_OPTIMIZESPEED ||
@@ -798,7 +798,7 @@ SVGGeometryFrame::Render(gfxContext* aContext,
     }
   }
 
-  SVGContextPaint* contextPaint = SVGContextPaint::GetContextPaint(mContent);
+  SVGContextPaint* contextPaint = SVGContextPaint::GetContextPaint(GetContent());
 
   if (aRenderComponents & eRenderFill) {
     GeneralPattern fillPattern;
@@ -846,7 +846,7 @@ SVGGeometryFrame::Render(gfxContext* aContext,
     if (strokePattern.GetPattern()) {
       SVGContentUtils::AutoStrokeOptions strokeOptions;
       SVGContentUtils::GetStrokeOptions(&strokeOptions,
-                                        static_cast<nsSVGElement*>(mContent),
+                                        static_cast<nsSVGElement*>(GetContent()),
                                         StyleContext(), contextPaint);
       // GetStrokeOptions may set the line width to zero as an optimization
       if (strokeOptions.mLineWidth <= 0) {
@@ -871,8 +871,8 @@ SVGGeometryFrame::PaintMarkers(gfxContext& aContext,
                                const gfxMatrix& aTransform,
                                imgDrawingParams& aImgParams)
 {
-  SVGContextPaint* contextPaint = SVGContextPaint::GetContextPaint(mContent);
-  if (static_cast<SVGGeometryElement*>(mContent)->IsMarkable()) {
+  SVGContextPaint* contextPaint = SVGContextPaint::GetContextPaint(GetContent());
+  if (static_cast<SVGGeometryElement*>(GetContent())->IsMarkable()) {
     MarkerProperties properties = GetMarkerProperties(this);
 
     if (properties.MarkersExist()) {
@@ -880,7 +880,7 @@ SVGGeometryFrame::PaintMarkers(gfxContext& aContext,
 
       nsTArray<nsSVGMark> marks;
       static_cast<SVGGeometryElement*>
-                 (mContent)->GetMarkPoints(&marks);
+                 (GetContent())->GetMarkPoints(&marks);
 
       uint32_t num = marks.Length();
       if (num) {
diff --git a/layout/svg/SVGTextFrame.cpp b/layout/svg/SVGTextFrame.cpp
index abb6a4392184..affa4dfc98bb 100644
--- a/layout/svg/SVGTextFrame.cpp
+++ b/layout/svg/SVGTextFrame.cpp
@@ -3651,7 +3651,7 @@ SVGTextFrame::PaintSVG(gfxContext& aContext,
   TextRenderedRun run = it.Current();
 
   SVGContextPaint* outerContextPaint =
-    SVGContextPaint::GetContextPaint(mContent);
+    SVGContextPaint::GetContextPaint(GetContent());
 
   while (run.mFrame) {
     nsTextFrame* frame = run.mFrame;
@@ -3925,7 +3925,7 @@ SVGTextFrame::GetCanvasTM()
                  "should not call GetCanvasTM() when we are non-display");
 
     nsSVGContainerFrame *parent = static_cast<nsSVGContainerFrame*>(GetParent());
-    dom::SVGTextContentElement *content = static_cast<dom::SVGTextContentElement*>(mContent);
+    dom::SVGTextContentElement *content = static_cast<dom::SVGTextContentElement*>(GetContent());
 
     gfxMatrix tm = content->PrependLocalTransformsTo(parent->GetCanvasTM());
 
@@ -5059,7 +5059,7 @@ SVGTextFrame::DoGlyphPositioning()
 
   // If the textLength="" attribute was specified, then we need ResolvePositions
   // to record that a new run starts with each glyph.
-  SVGTextContentElement* element = static_cast<SVGTextContentElement*>(mContent);
+  SVGTextContentElement* element = static_cast<SVGTextContentElement*>(GetContent());
   nsSVGLength2* textLengthAttr =
     element->GetAnimatedLength(nsGkAtoms::textLength);
   bool adjustingTextLength = textLengthAttr->IsExplicitlySet();
@@ -5213,7 +5213,7 @@ SVGTextFrame::ShouldRenderAsPath(nsTextFrame* aFrame,
 
   // Text has a stroke.
   if (style->HasStroke() &&
-      SVGContentUtils::CoordToFloat(static_cast<nsSVGElement*>(mContent),
+      SVGContentUtils::CoordToFloat(static_cast<nsSVGElement*>(GetContent()),
                                     style->mStrokeWidth) > 0) {
     return true;
   }
diff --git a/layout/svg/nsSVGAFrame.cpp b/layout/svg/nsSVGAFrame.cpp
index c3342471e4a0..bcc0e8ce3509 100644
--- a/layout/svg/nsSVGAFrame.cpp
+++ b/layout/svg/nsSVGAFrame.cpp
@@ -103,7 +103,7 @@ nsSVGAFrame::AttributeChanged(int32_t         aNameSpaceID,
       (aNameSpaceID == kNameSpaceID_None ||
        aNameSpaceID == kNameSpaceID_XLink)) {
 
-    dom::SVGAElement* content = static_cast<dom::SVGAElement*>(mContent);
+    dom::SVGAElement* content = static_cast<dom::SVGAElement*>(GetContent());
 
     // SMIL may change whether an <a> element is a link, in which case we will
     // need to update the link state.
@@ -140,7 +140,7 @@ nsSVGAFrame::GetCanvasTM()
     NS_ASSERTION(GetParent(), "null parent");
 
     nsSVGContainerFrame *parent = static_cast<nsSVGContainerFrame*>(GetParent());
-    dom::SVGAElement *content = static_cast<dom::SVGAElement*>(mContent);
+    dom::SVGAElement *content = static_cast<dom::SVGAElement*>(GetContent());
 
     gfxMatrix tm = content->PrependLocalTransformsTo(parent->GetCanvasTM());
 
diff --git a/layout/svg/nsSVGClipPathFrame.cpp b/layout/svg/nsSVGClipPathFrame.cpp
index 8c1482425179..0411f3ccbc50 100644
--- a/layout/svg/nsSVGClipPathFrame.cpp
+++ b/layout/svg/nsSVGClipPathFrame.cpp
@@ -458,7 +458,7 @@ nsSVGClipPathFrame::GetCanvasTM()
 gfxMatrix
 nsSVGClipPathFrame::GetClipPathTransform(nsIFrame* aClippedFrame)
 {
-  SVGClipPathElement *content = static_cast<SVGClipPathElement*>(mContent);
+  SVGClipPathElement *content = static_cast<SVGClipPathElement*>(GetContent());
 
   gfxMatrix tm = content->PrependLocalTransformsTo(gfxMatrix());
 
diff --git a/layout/svg/nsSVGContainerFrame.cpp b/layout/svg/nsSVGContainerFrame.cpp
index ec319063b5c0..a154ab6fb135 100644
--- a/layout/svg/nsSVGContainerFrame.cpp
+++ b/layout/svg/nsSVGContainerFrame.cpp
@@ -147,7 +147,7 @@ nsSVGDisplayContainerFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
 {
   // mContent could be a XUL element so check for an SVG element before casting
   if (mContent->IsSVGElement() &&
-      !static_cast<const nsSVGElement*>(mContent)->HasValidDimensions()) {
+      !static_cast<const nsSVGElement*>(GetContent())->HasValidDimensions()) {
     return;
   }
   DisplayOutline(aBuilder, aLists);
@@ -232,7 +232,7 @@ nsSVGDisplayContainerFrame::IsSVGTransformed(gfx::Matrix *aOwnTransform,
 
   // mContent could be a XUL element so check for an SVG element before casting
   if (mContent->IsSVGElement()) {
-    nsSVGElement *content = static_cast<nsSVGElement*>(mContent);
+    nsSVGElement *content = static_cast<nsSVGElement*>(GetContent());
     nsSVGAnimatedTransformList* transformList =
       content->GetAnimatedTransformList();
     if ((transformList && transformList->HasTransform()) ||
diff --git a/layout/svg/nsSVGFilterFrame.cpp b/layout/svg/nsSVGFilterFrame.cpp
index 524f8d207ddb..292efde71c93 100644
--- a/layout/svg/nsSVGFilterFrame.cpp
+++ b/layout/svg/nsSVGFilterFrame.cpp
@@ -33,7 +33,7 @@ uint16_t
 nsSVGFilterFrame::GetEnumValue(uint32_t aIndex, nsIContent *aDefault)
 {
   nsSVGEnum& thisEnum =
-    static_cast<SVGFilterElement *>(mContent)->mEnumAttributes[aIndex];
+    static_cast<SVGFilterElement *>(GetContent())->mEnumAttributes[aIndex];
 
   if (thisEnum.IsExplicitlySet())
     return thisEnum.GetAnimValue();
@@ -60,7 +60,7 @@ const nsSVGLength2 *
 nsSVGFilterFrame::GetLengthValue(uint32_t aIndex, nsIContent *aDefault)
 {
   const nsSVGLength2 *thisLength =
-    &static_cast<SVGFilterElement *>(mContent)->mLengthAttributes[aIndex];
+    &static_cast<SVGFilterElement *>(GetContent())->mLengthAttributes[aIndex];
 
   if (thisLength->IsExplicitlySet())
     return thisLength;
@@ -90,7 +90,7 @@ nsSVGFilterFrame::GetFilterContent(nsIContent *aDefault)
     RefPtr<nsSVGFE> primitive;
     CallQueryInterface(child, (nsSVGFE**)getter_AddRefs(primitive));
     if (primitive) {
-      return static_cast<SVGFilterElement *>(mContent);
+      return static_cast<SVGFilterElement *>(GetContent());
     }
   }
 
@@ -121,7 +121,7 @@ nsSVGFilterFrame::GetReferencedFilter()
 
   if (!property) {
     // Fetch our Filter element's href or xlink:href attribute
-    SVGFilterElement *filter = static_cast<SVGFilterElement *>(mContent);
+    SVGFilterElement *filter = static_cast<SVGFilterElement *>(GetContent());
     nsAutoString href;
     if (filter->mStringAttributes[SVGFilterElement::HREF].IsExplicitlySet()) {
       filter->mStringAttributes[SVGFilterElement::HREF]
diff --git a/layout/svg/nsSVGForeignObjectFrame.cpp b/layout/svg/nsSVGForeignObjectFrame.cpp
index 4116457a8274..f5633d51b408 100644
--- a/layout/svg/nsSVGForeignObjectFrame.cpp
+++ b/layout/svg/nsSVGForeignObjectFrame.cpp
@@ -158,7 +158,7 @@ void
 nsSVGForeignObjectFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                           const nsDisplayListSet& aLists)
 {
-  if (!static_cast<const nsSVGElement*>(mContent)->HasValidDimensions()) {
+  if (!static_cast<const nsSVGElement*>(GetContent())->HasValidDimensions()) {
     return;
   }
   DisplayOutline(aBuilder, aLists);
@@ -179,7 +179,7 @@ nsSVGForeignObjectFrame::IsSVGTransformed(Matrix *aOwnTransform,
                        HasChildrenOnlyTransform(aFromParentTransform);
   }
 
-  nsSVGElement *content = static_cast<nsSVGElement*>(mContent);
+  nsSVGElement *content = static_cast<nsSVGElement*>(GetContent());
   nsSVGAnimatedTransformList* transformList =
     content->GetAnimatedTransformList();
   if ((transformList && transformList->HasTransform()) ||
@@ -251,7 +251,7 @@ nsSVGForeignObjectFrame::PaintSVG(gfxContext& aContext,
 
   if (StyleDisplay()->IsScrollableOverflow()) {
     float x, y, width, height;
-    static_cast<nsSVGElement*>(mContent)->
+    static_cast<nsSVGElement*>(GetContent())->
       GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
 
     gfxRect clipRect =
@@ -301,7 +301,7 @@ nsSVGForeignObjectFrame::GetFrameForPoint(const gfxPoint& aPoint)
     return nullptr;
 
   float x, y, width, height;
-  static_cast<nsSVGElement*>(mContent)->
+  static_cast<nsSVGElement*>(GetContent())->
     GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
 
   if (!gfxRect(x, y, width, height).Contains(aPoint) ||
@@ -335,7 +335,7 @@ nsSVGForeignObjectFrame::ReflowSVG()
   // correct dimensions:
 
   float x, y, w, h;
-  static_cast<SVGForeignObjectElement*>(mContent)->
+  static_cast<SVGForeignObjectElement*>(GetContent())->
     GetAnimatedLengthValues(&x, &y, &w, &h, nullptr);
 
   // If mRect's width or height are negative, reflow blows up! We must clamp!
@@ -392,7 +392,7 @@ nsSVGForeignObjectFrame::NotifySVGChanged(uint32_t aFlags)
 
   if (aFlags & COORD_CONTEXT_CHANGED) {
     SVGForeignObjectElement *fO =
-      static_cast<SVGForeignObjectElement*>(mContent);
+      static_cast<SVGForeignObjectElement*>(GetContent());
     // Coordinate context changes affect mCanvasTM if we have a
     // percentage 'x' or 'y'
     if (fO->mLengthAttributes[SVGForeignObjectElement::ATTR_X].IsPercentage() ||
@@ -455,7 +455,7 @@ nsSVGForeignObjectFrame::GetBBoxContribution(const Matrix &aToBBoxUserspace,
                                              uint32_t aFlags)
 {
   SVGForeignObjectElement *content =
-    static_cast<SVGForeignObjectElement*>(mContent);
+    static_cast<SVGForeignObjectElement*>(GetContent());
 
   float x, y, w, h;
   content->GetAnimatedLengthValues(&x, &y, &w, &h, nullptr);
@@ -480,7 +480,7 @@ nsSVGForeignObjectFrame::GetCanvasTM()
 
     nsSVGContainerFrame *parent = static_cast<nsSVGContainerFrame*>(GetParent());
     SVGForeignObjectElement *content =
-      static_cast<SVGForeignObjectElement*>(mContent);
+      static_cast<SVGForeignObjectElement*>(GetContent());
 
     gfxMatrix tm = content->PrependLocalTransformsTo(parent->GetCanvasTM());
 
diff --git a/layout/svg/nsSVGGFrame.cpp b/layout/svg/nsSVGGFrame.cpp
index 9be113a57066..91da2c98135c 100644
--- a/layout/svg/nsSVGGFrame.cpp
+++ b/layout/svg/nsSVGGFrame.cpp
@@ -65,7 +65,7 @@ nsSVGGFrame::GetCanvasTM()
     NS_ASSERTION(GetParent(), "null parent");
 
     nsSVGContainerFrame *parent = static_cast<nsSVGContainerFrame*>(GetParent());
-    SVGGraphicsElement *content = static_cast<SVGGraphicsElement*>(mContent);
+    SVGGraphicsElement *content = static_cast<SVGGraphicsElement*>(GetContent());
 
     gfxMatrix tm = content->PrependLocalTransformsTo(parent->GetCanvasTM());
 
diff --git a/layout/svg/nsSVGGradientFrame.cpp b/layout/svg/nsSVGGradientFrame.cpp
index b1a9b1b771cd..a0d88f4d3fe6 100644
--- a/layout/svg/nsSVGGradientFrame.cpp
+++ b/layout/svg/nsSVGGradientFrame.cpp
@@ -67,7 +67,7 @@ uint16_t
 nsSVGGradientFrame::GetEnumValue(uint32_t aIndex, nsIContent *aDefault)
 {
   const nsSVGEnum& thisEnum =
-    static_cast<dom::SVGGradientElement*>(mContent)->mEnumAttributes[aIndex];
+    static_cast<dom::SVGGradientElement*>(GetContent())->mEnumAttributes[aIndex];
 
   if (thisEnum.IsExplicitlySet())
     return thisEnum.GetAnimValue();
@@ -107,7 +107,7 @@ const nsSVGAnimatedTransformList*
 nsSVGGradientFrame::GetGradientTransformList(nsIContent* aDefault)
 {
   nsSVGAnimatedTransformList *thisTransformList =
-    static_cast<dom::SVGGradientElement*>(mContent)->GetAnimatedTransformList();
+    static_cast<dom::SVGGradientElement*>(GetContent())->GetAnimatedTransformList();
 
   if (thisTransformList && thisTransformList->IsExplicitlySet())
     return thisTransformList;
@@ -152,7 +152,7 @@ nsSVGGradientFrame::GetGradientTransform(nsIFrame *aSource,
   }
 
   const nsSVGAnimatedTransformList* animTransformList =
-    GetGradientTransformList(mContent);
+    GetGradientTransformList(GetContent());
   if (!animTransformList)
     return bboxMatrix;
 
@@ -340,7 +340,7 @@ nsSVGGradientFrame::GetReferencedGradient()
   if (!property) {
     // Fetch our gradient element's href or xlink:href attribute
     dom::SVGGradientElement* grad =
-      static_cast<dom::SVGGradientElement*>(mContent);
+      static_cast<dom::SVGGradientElement*>(GetContent());
     nsAutoString href;
     if (grad->mStringAttributes[dom::SVGGradientElement::HREF]
           .IsExplicitlySet()) {
@@ -454,7 +454,7 @@ nsSVGLinearGradientFrame::GetLengthValue(uint32_t aIndex)
 {
   dom::SVGLinearGradientElement* lengthElement =
     GetLinearGradientWithLength(aIndex,
-      static_cast<dom::SVGLinearGradientElement*>(mContent));
+      static_cast<dom::SVGLinearGradientElement*>(GetContent()));
   // We passed in mContent as a fallback, so, assuming mContent is non-null, the
   // return value should also be non-null.
   MOZ_ASSERT(lengthElement,
@@ -482,7 +482,7 @@ nsSVGLinearGradientFrame::GetLinearGradientWithLength(uint32_t aIndex,
   dom::SVGLinearGradientElement* aDefault)
 {
   dom::SVGLinearGradientElement* thisElement =
-    static_cast<dom::SVGLinearGradientElement*>(mContent);
+    static_cast<dom::SVGLinearGradientElement*>(GetContent());
   const nsSVGLength2 &length = thisElement->mLengthAttributes[aIndex];
 
   if (length.IsExplicitlySet()) {
@@ -557,7 +557,7 @@ nsSVGRadialGradientFrame::GetLengthValue(uint32_t aIndex)
 {
   dom::SVGRadialGradientElement* lengthElement =
     GetRadialGradientWithLength(aIndex,
-      static_cast<dom::SVGRadialGradientElement*>(mContent));
+      static_cast<dom::SVGRadialGradientElement*>(GetContent()));
   // We passed in mContent as a fallback, so, assuming mContent is non-null,
   // the return value should also be non-null.
   MOZ_ASSERT(lengthElement,
@@ -602,7 +602,7 @@ nsSVGRadialGradientFrame::GetRadialGradientWithLength(uint32_t aIndex,
   dom::SVGRadialGradientElement* aDefault)
 {
   dom::SVGRadialGradientElement* thisElement =
-    static_cast<dom::SVGRadialGradientElement*>(mContent);
+    static_cast<dom::SVGRadialGradientElement*>(GetContent());
   const nsSVGLength2 &length = thisElement->mLengthAttributes[aIndex];
 
   if (length.IsExplicitlySet()) {
diff --git a/layout/svg/nsSVGImageFrame.cpp b/layout/svg/nsSVGImageFrame.cpp
index 074415854667..12b82ce1fd7c 100644
--- a/layout/svg/nsSVGImageFrame.cpp
+++ b/layout/svg/nsSVGImageFrame.cpp
@@ -49,7 +49,7 @@ nsSVGImageFrame::~nsSVGImageFrame()
 {
   // set the frame to null so we don't send messages to a dead object.
   if (mListener) {
-    nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(mContent);
+    nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(GetContent());
     if (imageLoader) {
       imageLoader->RemoveNativeObserver(mListener);
     }
@@ -81,7 +81,7 @@ nsSVGImageFrame::Init(nsIContent*       aContent,
   }
 
   mListener = new nsSVGImageListener(this);
-  nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(mContent);
+  nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(GetContent());
   if (!imageLoader) {
     MOZ_CRASH("Why is this not an image loading content?");
   }
@@ -151,7 +151,7 @@ nsSVGImageFrame::AttributeChanged(int32_t         aNameSpaceID,
       aAttribute == nsGkAtoms::href &&
       (aNameSpaceID == kNameSpaceID_XLink ||
        aNameSpaceID == kNameSpaceID_None)) {
-    SVGImageElement* element = static_cast<SVGImageElement*>(mContent);
+    SVGImageElement* element = static_cast<SVGImageElement*>(GetContent());
 
     bool hrefIsSet =
       element->mStringAttributes[SVGImageElement::HREF].IsExplicitlySet() ||
@@ -171,7 +171,7 @@ void
 nsSVGImageFrame::OnVisibilityChange(Visibility aNewVisibility,
                                     const Maybe<OnNonvisible>& aNonvisibleAction)
 {
-  nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(mContent);
+  nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(GetContent());
   if (!imageLoader) {
     SVGGeometryFrame::OnVisibilityChange(aNewVisibility, aNonvisibleAction);
     return;
@@ -187,7 +187,7 @@ nsSVGImageFrame::GetRasterImageTransform(int32_t aNativeWidth,
                                          int32_t aNativeHeight)
 {
   float x, y, width, height;
-  SVGImageElement *element = static_cast<SVGImageElement*>(mContent);
+  SVGImageElement *element = static_cast<SVGImageElement*>(GetContent());
   element->GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
 
   Matrix viewBoxTM =
@@ -202,7 +202,7 @@ gfx::Matrix
 nsSVGImageFrame::GetVectorImageTransform()
 {
   float x, y, width, height;
-  SVGImageElement *element = static_cast<SVGImageElement*>(mContent);
+  SVGImageElement *element = static_cast<SVGImageElement*>(GetContent());
   element->GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
 
   // No viewBoxTM needed here -- our height/width overrides any concept of
@@ -258,14 +258,14 @@ nsSVGImageFrame::PaintSVG(gfxContext& aContext,
   }
 
   float x, y, width, height;
-  SVGImageElement *imgElem = static_cast<SVGImageElement*>(mContent);
+  SVGImageElement *imgElem = static_cast<SVGImageElement*>(GetContent());
   imgElem->GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
   NS_ASSERTION(width > 0 && height > 0,
                "Should only be painting things with valid width/height");
 
   if (!mImageContainer) {
     nsCOMPtr<imgIRequest> currentRequest;
-    nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(mContent);
+    nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(GetContent());
     if (imageLoader)
       imageLoader->GetRequest(nsIImageLoadingContent::CURRENT_REQUEST,
                               getter_AddRefs(currentRequest));
@@ -374,7 +374,7 @@ nsSVGImageFrame::GetFrameForPoint(const gfxPoint& aPoint)
   }
 
   Rect rect;
-  SVGImageElement *element = static_cast<SVGImageElement*>(mContent);
+  SVGImageElement *element = static_cast<SVGImageElement*>(GetContent());
   element->GetAnimatedLengthValues(&rect.x, &rect.y,
                                    &rect.width, &rect.height, nullptr);
 
@@ -432,7 +432,7 @@ nsSVGImageFrame::ReflowSVG()
   }
 
   float x, y, width, height;
-  SVGImageElement *element = static_cast<SVGImageElement*>(mContent);
+  SVGImageElement *element = static_cast<SVGImageElement*>(GetContent());
   element->GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
 
   Rect extent(x, y, width, height);
diff --git a/layout/svg/nsSVGMarkerFrame.cpp b/layout/svg/nsSVGMarkerFrame.cpp
index dbeb02ea5b2d..9fdefbea7976 100644
--- a/layout/svg/nsSVGMarkerFrame.cpp
+++ b/layout/svg/nsSVGMarkerFrame.cpp
@@ -74,7 +74,7 @@ nsSVGMarkerFrame::GetCanvasTM()
     return gfxMatrix();
   }
 
-  SVGMarkerElement *content = static_cast<SVGMarkerElement*>(mContent);
+  SVGMarkerElement *content = static_cast<SVGMarkerElement*>(GetContent());
 
   mInUse2 = true;
   gfxMatrix markedTM = mMarkedFrame->GetCanvasTM();
@@ -110,7 +110,7 @@ nsSVGMarkerFrame::PaintMark(gfxContext& aContext,
 
   AutoMarkerReferencer markerRef(this, aMarkedFrame);
 
-  SVGMarkerElement *marker = static_cast<SVGMarkerElement*>(mContent);
+  SVGMarkerElement *marker = static_cast<SVGMarkerElement*>(GetContent());
   if (!marker->HasValidDimensions()) {
     return;
   }
@@ -165,7 +165,7 @@ nsSVGMarkerFrame::GetMarkBBoxContribution(const Matrix& aToBBoxUserspace,
 
   AutoMarkerReferencer markerRef(this, aMarkedFrame);
 
-  SVGMarkerElement *content = static_cast<SVGMarkerElement*>(mContent);
+  SVGMarkerElement *content = static_cast<SVGMarkerElement*>(GetContent());
   if (!content->HasValidDimensions()) {
     return bbox;
   }
@@ -196,7 +196,7 @@ nsSVGMarkerFrame::GetMarkBBoxContribution(const Matrix& aToBBoxUserspace,
 void
 nsSVGMarkerFrame::SetParentCoordCtxProvider(SVGSVGElement *aContext)
 {
-  SVGMarkerElement *marker = static_cast<SVGMarkerElement*>(mContent);
+  SVGMarkerElement *marker = static_cast<SVGMarkerElement*>(GetContent());
   marker->SetParentCoordCtxProvider(aContext);
 }
 
diff --git a/layout/svg/nsSVGMaskFrame.cpp b/layout/svg/nsSVGMaskFrame.cpp
index 42b3171982a7..aa3a2c6cc135 100644
--- a/layout/svg/nsSVGMaskFrame.cpp
+++ b/layout/svg/nsSVGMaskFrame.cpp
@@ -160,7 +160,7 @@ nsSVGMaskFrame::GetMaskForMaskedFrame(MaskParams& aParams)
 gfxRect
 nsSVGMaskFrame::GetMaskArea(nsIFrame* aMaskedFrame)
 {
-  SVGMaskElement *maskElem = static_cast<SVGMaskElement*>(mContent);
+  SVGMaskElement *maskElem = static_cast<SVGMaskElement*>(GetContent());
 
   uint16_t units =
     maskElem->mEnumAttributes[SVGMaskElement::MASKUNITS].GetAnimValue();
@@ -221,7 +221,7 @@ nsSVGMaskFrame::GetCanvasTM()
 gfxMatrix
 nsSVGMaskFrame::GetMaskTransform(nsIFrame* aMaskedFrame)
 {
-  SVGMaskElement *content = static_cast<SVGMaskElement*>(mContent);
+  SVGMaskElement *content = static_cast<SVGMaskElement*>(GetContent());
 
   nsSVGEnum* maskContentUnits =
     &content->mEnumAttributes[SVGMaskElement::MASKCONTENTUNITS];
diff --git a/layout/svg/nsSVGOuterSVGFrame.cpp b/layout/svg/nsSVGOuterSVGFrame.cpp
index 6c01c95eba2a..6382d2c1f918 100644
--- a/layout/svg/nsSVGOuterSVGFrame.cpp
+++ b/layout/svg/nsSVGOuterSVGFrame.cpp
@@ -168,7 +168,7 @@ nsSVGOuterSVGFrame::GetPrefISize(gfxContext *aRenderingContext)
   nscoord result;
   DISPLAY_PREF_WIDTH(this, result);
 
-  SVGSVGElement *svg = static_cast<SVGSVGElement*>(mContent);
+  SVGSVGElement *svg = static_cast<SVGSVGElement*>(GetContent());
   WritingMode wm = GetWritingMode();
   const nsSVGLength2& isize = wm.IsVertical()
     ? svg->mLengthAttributes[SVGSVGElement::ATTR_HEIGHT]
@@ -212,7 +212,7 @@ nsSVGOuterSVGFrame::GetIntrinsicSize()
 
   IntrinsicSize intrinsicSize;
 
-  SVGSVGElement *content = static_cast<SVGSVGElement*>(mContent);
+  SVGSVGElement *content = static_cast<SVGSVGElement*>(GetContent());
   const nsSVGLength2& width =
     content->mLengthAttributes[SVGSVGElement::ATTR_WIDTH];
   const nsSVGLength2& height =
@@ -240,7 +240,7 @@ nsSVGOuterSVGFrame::GetIntrinsicRatio()
   // are both specified and set to non-percentage values, or we have a viewBox
   // rect: http://www.w3.org/TR/SVGMobile12/coords.html#IntrinsicSizing
 
-  SVGSVGElement *content = static_cast<SVGSVGElement*>(mContent);
+  SVGSVGElement *content = static_cast<SVGSVGElement*>(GetContent());
   const nsSVGLength2& width =
     content->mLengthAttributes[SVGSVGElement::ATTR_WIDTH];
   const nsSVGLength2& height =
@@ -324,7 +324,7 @@ nsSVGOuterSVGFrame::ComputeSize(gfxContext *aRenderingContext,
     // intrinsic size.  Also note that explicit percentage values are mapped
     // into style, so the following isn't for them.)
 
-    SVGSVGElement* content = static_cast<SVGSVGElement*>(mContent);
+    SVGSVGElement* content = static_cast<SVGSVGElement*>(GetContent());
 
     const nsSVGLength2& width =
       content->mLengthAttributes[SVGSVGElement::ATTR_WIDTH];
@@ -383,7 +383,7 @@ nsSVGOuterSVGFrame::Reflow(nsPresContext*           aPresContext,
 
   NS_ASSERTION(!GetPrevInFlow(), "SVG can't currently be broken across pages.");
 
-  SVGSVGElement *svgElem = static_cast<SVGSVGElement*>(mContent);
+  SVGSVGElement *svgElem = static_cast<SVGSVGElement*>(GetContent());
 
   nsSVGOuterSVGAnonChildFrame *anonKid =
     static_cast<nsSVGOuterSVGAnonChildFrame*>(PrincipalChildList().FirstChild());
@@ -703,7 +703,7 @@ nsSVGOuterSVGFrame::AttributeChanged(int32_t  aNameSpaceID,
                   TRANSFORM_CHANGED | COORD_CONTEXT_CHANGED : TRANSFORM_CHANGED);
 
       if (aAttribute != nsGkAtoms::transform) {
-        static_cast<SVGSVGElement*>(mContent)->ChildrenOnlyTransformChanged();
+        static_cast<SVGSVGElement*>(GetContent())->ChildrenOnlyTransformChanged();
       }
 
     } else if (aAttribute == nsGkAtoms::width ||
@@ -743,7 +743,7 @@ nsSVGOuterSVGFrame::IsSVGTransformed(Matrix* aOwnTransform,
 
   bool foundTransform = false;
 
-  SVGSVGElement *content = static_cast<SVGSVGElement*>(mContent);
+  SVGSVGElement *content = static_cast<SVGSVGElement*>(GetContent());
   nsSVGAnimatedTransformList* transformList =
     content->GetAnimatedTransformList();
   if ((transformList && transformList->HasTransform()) ||
@@ -816,7 +816,7 @@ nsSVGOuterSVGFrame::NotifyViewportOrTransformChanged(uint32_t aFlags)
     return;
   }
 
-  SVGSVGElement *content = static_cast<SVGSVGElement*>(mContent);
+  SVGSVGElement *content = static_cast<SVGSVGElement*>(GetContent());
 
   if (aFlags & COORD_CONTEXT_CHANGED) {
     if (content->HasViewBoxRect()) {
@@ -900,7 +900,7 @@ gfxMatrix
 nsSVGOuterSVGFrame::GetCanvasTM()
 {
   if (!mCanvasTM) {
-    SVGSVGElement *content = static_cast<SVGSVGElement*>(mContent);
+    SVGSVGElement *content = static_cast<SVGSVGElement*>(GetContent());
 
     float devPxPerCSSPx =
       1.0f / PresContext()->AppUnitsToFloatCSSPixels(
@@ -967,7 +967,7 @@ nsSVGOuterSVGFrame::IsRootOfImage()
 bool
 nsSVGOuterSVGFrame::VerticalScrollbarNotNeeded() const
 {
-  const nsSVGLength2& height = static_cast<SVGSVGElement*>(mContent)->
+  const nsSVGLength2& height = static_cast<SVGSVGElement*>(GetContent())->
                                  mLengthAttributes[SVGSVGElement::ATTR_HEIGHT];
   return height.IsPercentage() && height.GetBaseValInSpecifiedUnits() <= 100;
 }
@@ -1012,7 +1012,7 @@ nsSVGOuterSVGAnonChildFrame::IsSVGTransformed(Matrix* aOwnTransform,
   // anonymous child frame. Since we are the child frame, we apply the
   // children-only transforms as if they are our own transform.
 
-  SVGSVGElement* content = static_cast<SVGSVGElement*>(mContent);
+  SVGSVGElement* content = static_cast<SVGSVGElement*>(GetContent());
 
   if (!content->HasChildrenOnlyTransform()) {
     return false;
diff --git a/layout/svg/nsSVGPatternFrame.cpp b/layout/svg/nsSVGPatternFrame.cpp
index 488ac2f5c783..805f21d9a38c 100644
--- a/layout/svg/nsSVGPatternFrame.cpp
+++ b/layout/svg/nsSVGPatternFrame.cpp
@@ -440,7 +440,7 @@ uint16_t
 nsSVGPatternFrame::GetEnumValue(uint32_t aIndex, nsIContent *aDefault)
 {
   nsSVGEnum& thisEnum =
-    static_cast<SVGPatternElement *>(mContent)->mEnumAttributes[aIndex];
+    static_cast<SVGPatternElement *>(GetContent())->mEnumAttributes[aIndex];
 
   if (thisEnum.IsExplicitlySet())
     return thisEnum.GetAnimValue();
@@ -466,7 +466,7 @@ nsSVGAnimatedTransformList*
 nsSVGPatternFrame::GetPatternTransformList(nsIContent* aDefault)
 {
   nsSVGAnimatedTransformList *thisTransformList =
-    static_cast<SVGPatternElement *>(mContent)->GetAnimatedTransformList();
+    static_cast<SVGPatternElement *>(GetContent())->GetAnimatedTransformList();
 
   if (thisTransformList && thisTransformList->IsExplicitlySet())
     return thisTransformList;
@@ -490,7 +490,7 @@ gfxMatrix
 nsSVGPatternFrame::GetPatternTransform()
 {
   nsSVGAnimatedTransformList* animTransformList =
-    GetPatternTransformList(mContent);
+    GetPatternTransformList(GetContent());
   if (!animTransformList)
     return gfxMatrix();
 
@@ -501,7 +501,7 @@ const nsSVGViewBox &
 nsSVGPatternFrame::GetViewBox(nsIContent* aDefault)
 {
   const nsSVGViewBox &thisViewBox =
-    static_cast<SVGPatternElement *>(mContent)->mViewBox;
+    static_cast<SVGPatternElement *>(GetContent())->mViewBox;
 
   if (thisViewBox.IsExplicitlySet())
     return thisViewBox;
@@ -525,7 +525,7 @@ const SVGAnimatedPreserveAspectRatio &
 nsSVGPatternFrame::GetPreserveAspectRatio(nsIContent *aDefault)
 {
   const SVGAnimatedPreserveAspectRatio &thisPar =
-    static_cast<SVGPatternElement *>(mContent)->mPreserveAspectRatio;
+    static_cast<SVGPatternElement *>(GetContent())->mPreserveAspectRatio;
 
   if (thisPar.IsExplicitlySet())
     return thisPar;
@@ -549,7 +549,7 @@ const nsSVGLength2 *
 nsSVGPatternFrame::GetLengthValue(uint32_t aIndex, nsIContent *aDefault)
 {
   const nsSVGLength2 *thisLength =
-    &static_cast<SVGPatternElement *>(mContent)->mLengthAttributes[aIndex];
+    &static_cast<SVGPatternElement *>(GetContent())->mLengthAttributes[aIndex];
 
   if (thisLength->IsExplicitlySet())
     return thisLength;
@@ -581,7 +581,7 @@ nsSVGPatternFrame::GetReferencedPattern()
 
   if (!property) {
     // Fetch our pattern element's href or xlink:href attribute
-    SVGPatternElement *pattern = static_cast<SVGPatternElement *>(mContent);
+    SVGPatternElement *pattern = static_cast<SVGPatternElement *>(GetContent());
     nsAutoString href;
     if (pattern->mStringAttributes[SVGPatternElement::HREF].IsExplicitlySet()) {
       pattern->mStringAttributes[SVGPatternElement::HREF]
diff --git a/layout/svg/nsSVGSwitchFrame.cpp b/layout/svg/nsSVGSwitchFrame.cpp
index e320cfcbce97..2375f057ad20 100644
--- a/layout/svg/nsSVGSwitchFrame.cpp
+++ b/layout/svg/nsSVGSwitchFrame.cpp
@@ -130,7 +130,7 @@ nsSVGSwitchFrame::GetFrameForPoint(const gfxPoint& aPoint)
     // Transform the point from our SVG user space to our child's.
     gfxPoint point = aPoint;
     gfxMatrix m =
-      static_cast<const nsSVGElement*>(mContent)->
+      static_cast<const nsSVGElement*>(GetContent())->
         PrependLocalTransformsTo(gfxMatrix(), eChildToUserSpace);
     m = static_cast<const nsSVGElement*>(kid->GetContent())->
           PrependLocalTransformsTo(m, eUserSpaceToParent);
@@ -227,7 +227,7 @@ nsIFrame *
 nsSVGSwitchFrame::GetActiveChildFrame()
 {
   nsIContent *activeChild =
-    static_cast<mozilla::dom::SVGSwitchElement*>(mContent)->GetActiveChild();
+    static_cast<mozilla::dom::SVGSwitchElement*>(GetContent())->GetActiveChild();
 
   if (activeChild) {
     for (nsIFrame* kid = mFrames.FirstChild(); kid;
diff --git a/layout/svg/nsSVGUseFrame.cpp b/layout/svg/nsSVGUseFrame.cpp
index 75f4fd5418c1..3172d4a371f0 100644
--- a/layout/svg/nsSVGUseFrame.cpp
+++ b/layout/svg/nsSVGUseFrame.cpp
@@ -100,7 +100,7 @@ nsSVGUseFrame::AttributeChanged(int32_t         aNameSpaceID,
                                 nsIAtom*        aAttribute,
                                 int32_t         aModType)
 {
-  SVGUseElement *useElement = static_cast<SVGUseElement*>(mContent);
+  SVGUseElement *useElement = static_cast<SVGUseElement*>(GetContent());
 
   if (aNameSpaceID == kNameSpaceID_None) {
     if (aAttribute == nsGkAtoms::x || aAttribute == nsGkAtoms::y) {
@@ -150,7 +150,7 @@ nsSVGUseFrame::AttributeChanged(int32_t         aNameSpaceID,
 void
 nsSVGUseFrame::DestroyFrom(nsIFrame* aDestructRoot)
 {
-  RefPtr<SVGUseElement> use = static_cast<SVGUseElement*>(mContent);
+  RefPtr<SVGUseElement> use = static_cast<SVGUseElement*>(GetContent());
   nsSVGGFrame::DestroyFrom(aDestructRoot);
   use->DestroyAnonymousContent();
 }
@@ -166,7 +166,7 @@ nsSVGUseFrame::ReflowSVG()
   // handled by the nsSVGOuterSVGFrame for the anonymous <svg> that will be
   // created for that purpose.
   float x, y;
-  static_cast<SVGUseElement*>(mContent)->
+  static_cast<SVGUseElement*>(GetContent())->
     GetAnimatedLengthValues(&x, &y, nullptr);
   mRect.MoveTo(nsLayoutUtils::RoundGfxRectToAppRect(
                  gfxRect(x, y, 0.0, 0.0),
@@ -188,7 +188,7 @@ nsSVGUseFrame::NotifySVGChanged(uint32_t aFlags)
       !(aFlags & TRANSFORM_CHANGED)) {
     // Coordinate context changes affect mCanvasTM if we have a
     // percentage 'x' or 'y'
-    SVGUseElement *use = static_cast<SVGUseElement*>(mContent);
+    SVGUseElement *use = static_cast<SVGUseElement*>(GetContent());
     if (use->mLengthAttributes[SVGUseElement::ATTR_X].IsPercentage() ||
         use->mLengthAttributes[SVGUseElement::ATTR_Y].IsPercentage()) {
       aFlags |= TRANSFORM_CHANGED;
@@ -215,7 +215,7 @@ nsSVGUseFrame::NotifySVGChanged(uint32_t aFlags)
 nsresult
 nsSVGUseFrame::CreateAnonymousContent(nsTArray<ContentInfo>& aElements)
 {
-  SVGUseElement *use = static_cast<SVGUseElement*>(mContent);
+  SVGUseElement *use = static_cast<SVGUseElement*>(GetContent());
 
   nsIContent* clone = use->CreateAnonymousContent();
   nsLayoutUtils::PostRestyleEvent(
@@ -231,7 +231,7 @@ void
 nsSVGUseFrame::AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
                                         uint32_t aFilter)
 {
-  SVGUseElement *use = static_cast<SVGUseElement*>(mContent);
+  SVGUseElement *use = static_cast<SVGUseElement*>(GetContent());
   nsIContent* clone = use->GetAnonymousContent();
   if (clone) {
     aElements.AppendElement(clone);
diff --git a/layout/svg/nsSVGViewportFrame.cpp b/layout/svg/nsSVGViewportFrame.cpp
index a61f2ad831fb..9b1a6cf26d1b 100644
--- a/layout/svg/nsSVGViewportFrame.cpp
+++ b/layout/svg/nsSVGViewportFrame.cpp
@@ -38,7 +38,7 @@ nsSVGViewportFrame::PaintSVG(gfxContext& aContext,
 
   if (StyleDisplay()->IsScrollableOverflow()) {
     float x, y, width, height;
-    static_cast<SVGViewportElement*>(mContent)->
+    static_cast<SVGViewportElement*>(GetContent())->
       GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
 
     if (width <= 0 || height <= 0) {
@@ -61,7 +61,7 @@ nsSVGViewportFrame::ReflowSVG()
   // mRect must be set before FinishAndStoreOverflow is called in order
   // for our overflow areas to be clipped correctly.
   float x, y, width, height;
-  static_cast<SVGViewportElement*>(mContent)->
+  static_cast<SVGViewportElement*>(GetContent())->
     GetAnimatedLengthValues(&x, &y, &width, &height, nullptr);
   mRect = nsLayoutUtils::RoundGfxRectToAppRect(
                            gfxRect(x, y, width, height),
@@ -84,7 +84,7 @@ nsSVGViewportFrame::NotifySVGChanged(uint32_t aFlags)
 
   if (aFlags & COORD_CONTEXT_CHANGED) {
 
-    SVGViewportElement *svg = static_cast<SVGViewportElement*>(mContent);
+    SVGViewportElement *svg = static_cast<SVGViewportElement*>(GetContent());
 
     bool xOrYIsPercentage =
       svg->mLengthAttributes[SVGViewportElement::ATTR_X].IsPercentage() ||
@@ -151,7 +151,7 @@ nsSVGViewportFrame::GetBBoxContribution(const Matrix &aToBBoxUserspace,
     // Ideally getClientRects/getBoundingClientRect should be consistent with
     // getBBox.
     float x, y, w, h;
-    static_cast<SVGViewportElement*>(mContent)->
+    static_cast<SVGViewportElement*>(GetContent())->
       GetAnimatedLengthValues(&x, &y, &w, &h, nullptr);
     if (w < 0.0f) w = 0.0f;
     if (h < 0.0f) h = 0.0f;
@@ -180,7 +180,7 @@ nsSVGViewportFrame::AttributeChanged(int32_t  aNameSpaceID,
   if (aNameSpaceID == kNameSpaceID_None &&
       !(GetStateBits() & NS_FRAME_IS_NONDISPLAY)) {
 
-    SVGViewportElement* content = static_cast<SVGViewportElement*>(mContent);
+    SVGViewportElement* content = static_cast<SVGViewportElement*>(GetContent());
 
     if (aAttribute == nsGkAtoms::width ||
         aAttribute == nsGkAtoms::height) {
@@ -249,7 +249,7 @@ nsSVGViewportFrame::GetFrameForPoint(const gfxPoint& aPoint)
 
   if (StyleDisplay()->IsScrollableOverflow()) {
     Rect clip;
-    static_cast<nsSVGElement*>(mContent)->
+    static_cast<nsSVGElement*>(GetContent())->
       GetAnimatedLengthValues(&clip.x, &clip.y,
                               &clip.width, &clip.height, nullptr);
     if (!clip.Contains(ToPoint(aPoint))) {
@@ -284,7 +284,7 @@ nsSVGViewportFrame::GetCanvasTM()
     NS_ASSERTION(GetParent(), "null parent");
 
     nsSVGContainerFrame *parent = static_cast<nsSVGContainerFrame*>(GetParent());
-    SVGViewportElement *content = static_cast<SVGViewportElement*>(mContent);
+    SVGViewportElement *content = static_cast<SVGViewportElement*>(GetContent());
 
     gfxMatrix tm = content->PrependLocalTransformsTo(parent->GetCanvasTM());
 
@@ -296,7 +296,7 @@ nsSVGViewportFrame::GetCanvasTM()
 bool
 nsSVGViewportFrame::HasChildrenOnlyTransform(gfx::Matrix *aTransform) const
 {
-  SVGViewportElement *content = static_cast<SVGViewportElement*>(mContent);
+  SVGViewportElement *content = static_cast<SVGViewportElement*>(GetContent());
 
   if (content->HasViewBoxOrSyntheticViewBox()) {
     // XXX Maybe return false if the transform is the identity transform?
diff --git a/layout/xul/nsMenuFrame.cpp b/layout/xul/nsMenuFrame.cpp
index db1edab35b5c..142db235f03f 100644
--- a/layout/xul/nsMenuFrame.cpp
+++ b/layout/xul/nsMenuFrame.cpp
@@ -704,7 +704,7 @@ nsMenuFrame::GetAnchor()
   }
 
   // Always return the menu's content if the anchor wasn't set or wasn't found.
-  return anchor && anchor->GetPrimaryFrame() ? anchor : mContent;
+  return anchor && anchor->GetPrimaryFrame() ? anchor : GetContent();
 }
 
 void