diff --git a/layout/forms/nsButtonFrameRenderer.cpp b/layout/forms/nsButtonFrameRenderer.cpp
index ffe8048000f9..84458fd7c382 100644
--- a/layout/forms/nsButtonFrameRenderer.cpp
+++ b/layout/forms/nsButtonFrameRenderer.cpp
@@ -409,9 +409,7 @@ nsButtonFrameRenderer::GetButtonInnerFocusMargin()
 
   if (mInnerFocusStyle) {
     const nsStyleMargin* margin = mInnerFocusStyle->StyleMargin();
-    if (!margin->GetMargin(innerFocusMargin)) {
-      NS_NOTYETIMPLEMENTED("percentage margin");
-    }
+    margin->GetMarginNoPercentage(innerFocusMargin);
   }
 
   return innerFocusMargin;
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 5c3fd4b420bb..9be773bbecd7 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -966,8 +966,7 @@ nsIFrame::GetUsedMargin() const
   if (m) {
     margin = *m;
   } else {
-    DebugOnly<bool> hasMargin = StyleMargin()->GetMargin(margin);
-    NS_ASSERTION(hasMargin, "We should have a margin here! (out of memory?)");
+    StyleMargin()->GetMarginNoPercentage(margin);
   }
   return margin;
 }
diff --git a/layout/style/nsRuleNode.cpp b/layout/style/nsRuleNode.cpp
index 714b68511dad..e7ae77d7591e 100644
--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -7217,7 +7217,6 @@ nsRuleNode::ComputeMarginData(void* aStartStruct,
     }
   }
 
-  margin->RecalcData();
   COMPUTE_END_RESET(Margin, margin)
 }
 
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
index e1f11bc9b175..3ed0ff057135 100644
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -255,8 +255,6 @@ static nscoord CalcCoord(const nsStyleCoord& aCoord,
 }
 
 nsStyleMargin::nsStyleMargin(StyleStructContext aContext)
-  : mHasCachedMargin(false)
-  , mCachedMargin(0, 0, 0, 0)
 {
   MOZ_COUNT_CTOR(nsStyleMargin);
   nsStyleCoord zero(0, nsStyleCoord::CoordConstructor);
@@ -267,8 +265,6 @@ nsStyleMargin::nsStyleMargin(StyleStructContext aContext)
 
 nsStyleMargin::nsStyleMargin(const nsStyleMargin& aSrc)
   : mMargin(aSrc.mMargin)
-  , mHasCachedMargin(false)
-  , mCachedMargin(0, 0, 0, 0)
 {
   MOZ_COUNT_CTOR(nsStyleMargin);
 }
@@ -280,19 +276,6 @@ nsStyleMargin::Destroy(nsPresContext* aContext) {
     FreeByObjectID(eArenaObjectID_nsStyleMargin, this);
 }
 
-
-void nsStyleMargin::RecalcData()
-{
-  if (mMargin.ConvertsToLength()) {
-    NS_FOR_CSS_SIDES(side) {
-      mCachedMargin.Side(side) = CalcCoord(mMargin.Get(side), nullptr, 0);
-    }
-    mHasCachedMargin = true;
-  }
-  else
-    mHasCachedMargin = false;
-}
-
 nsChangeHint nsStyleMargin::CalcDifference(const nsStyleMargin& aOther) const
 {
   if (mMargin == aOther.mMargin) {
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index 01131f819ed8..cca4193b19eb 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -853,7 +853,6 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleMargin
   }
   void Destroy(nsPresContext* aContext);
 
-  void RecalcData();
   nsChangeHint CalcDifference(const nsStyleMargin& aOther) const;
   static nsChangeHint MaxDifference() {
     return nsChangeHint_NeedReflow |
@@ -868,19 +867,27 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleMargin
 
   nsStyleSides  mMargin;          // [reset] coord, percent, calc, auto
 
-  bool IsWidthDependent() const { return !mHasCachedMargin; }
+  bool IsWidthDependent() const {
+    return !mMargin.ConvertsToLength();
+  }
+
   bool GetMargin(nsMargin& aMargin) const
   {
-    if (mHasCachedMargin) {
-      aMargin = mCachedMargin;
+    if (mMargin.ConvertsToLength()) {
+      GetMarginNoPercentage(aMargin);
       return true;
     }
+
     return false;
   }
 
-protected:
-  bool          mHasCachedMargin;
-  nsMargin      mCachedMargin;
+  void GetMarginNoPercentage(nsMargin& aMargin) const
+  {
+    MOZ_ASSERT(mMargin.ConvertsToLength());
+    NS_FOR_CSS_SIDES(side) {
+      aMargin.Side(side) = mMargin.Get(side).ToLength();
+    }
+  }
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStylePadding