--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -3421,39 +3421,16 @@ void
 StyleTransition::SetInitialValues()
 {
   mTimingFunction = nsTimingFunction(NS_STYLE_TRANSITION_TIMING_FUNCTION_EASE);
   mDuration = 0.0;
   mDelay = 0.0;
   mProperty = eCSSPropertyExtra_all_properties;
 }
 
-void
-StyleTransition::SetUnknownProperty(nsCSSPropertyID aProperty,
-                                    const nsAString& aPropertyString)
-{
-  MOZ_ASSERT(nsCSSProps::LookupProperty(aPropertyString,
-                                        CSSEnabledState::eForAllContent) ==
-               aProperty,
-             "property and property string should match");
-  RefPtr<nsAtom> temp = NS_Atomize(aPropertyString);
-  SetUnknownProperty(aProperty, temp);
-}
-
-void
-StyleTransition::SetUnknownProperty(nsCSSPropertyID aProperty,
-                                    nsAtom* aPropertyString)
-{
-  MOZ_ASSERT(aProperty == eCSSProperty_UNKNOWN ||
-             aProperty == eCSSPropertyExtra_variable,
-             "should be either unknown or custom property");
-  mProperty = aProperty;
-  mUnknownProperty = aPropertyString;
-}
-
 bool
 StyleTransition::operator==(const StyleTransition& aOther) const
 {
   return mTimingFunction == aOther.mTimingFunction &&
          mDuration == aOther.mDuration &&
          mDelay == aOther.mDelay &&
          mProperty == aOther.mProperty &&
          (mProperty != eCSSProperty_UNKNOWN ||

--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -1908,32 +1908,16 @@ struct StyleTransition
   float GetDuration() const { return mDuration; }
   nsCSSPropertyID GetProperty() const { return mProperty; }
   nsAtom* GetUnknownProperty() const { return mUnknownProperty; }
 
   void SetTimingFunction(const nsTimingFunction& aTimingFunction)
     { mTimingFunction = aTimingFunction; }
   void SetDelay(float aDelay) { mDelay = aDelay; }
   void SetDuration(float aDuration) { mDuration = aDuration; }
-  void SetProperty(nsCSSPropertyID aProperty)
-    {
-      NS_ASSERTION(aProperty != eCSSProperty_UNKNOWN &&
-                   aProperty != eCSSPropertyExtra_variable,
-                   "invalid property");
-      mProperty = aProperty;
-    }
-  void SetUnknownProperty(nsCSSPropertyID aProperty,
-                          const nsAString& aPropertyString);
-  void SetUnknownProperty(nsCSSPropertyID aProperty,
-                          nsAtom* aPropertyString);
-  void CopyPropertyFrom(const StyleTransition& aOther)
-    {
-      mProperty = aOther.mProperty;
-      mUnknownProperty = aOther.mUnknownProperty;
-    }
 
   nsTimingFunction& TimingFunctionSlot() { return mTimingFunction; }
 
   bool operator==(const StyleTransition& aOther) const;
   bool operator!=(const StyleTransition& aOther) const
     { return !(*this == aOther); }
 
 private: