--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -5184,17 +5184,17 @@ nsComputedDOMStyle::DoGetTransitionDelay
   const nsStyleDisplay* display = StyleDisplay();
 
   nsDOMCSSValueList *valueList = GetROCSSValueList(true);
 
   NS_ABORT_IF_FALSE(display->mTransitionDelayCount > 0,
                     "first item must be explicit");
   uint32_t i = 0;
   do {
-    const nsTransition *transition = &display->mTransitions[i];
+    const StyleTransition *transition = &display->mTransitions[i];
     nsROCSSPrimitiveValue* delay = new nsROCSSPrimitiveValue;
     valueList->AppendCSSValue(delay);
     delay->SetTime((float)transition->GetDelay() / (float)PR_MSEC_PER_SEC);
   } while (++i < display->mTransitionDelayCount);
 
   return valueList;
 }
 
@@ -5204,17 +5204,17 @@ nsComputedDOMStyle::DoGetTransitionDurat
   const nsStyleDisplay* display = StyleDisplay();
 
   nsDOMCSSValueList *valueList = GetROCSSValueList(true);
 
   NS_ABORT_IF_FALSE(display->mTransitionDurationCount > 0,
                     "first item must be explicit");
   uint32_t i = 0;
   do {
-    const nsTransition *transition = &display->mTransitions[i];
+    const StyleTransition *transition = &display->mTransitions[i];
     nsROCSSPrimitiveValue* duration = new nsROCSSPrimitiveValue;
     valueList->AppendCSSValue(duration);
 
     duration->SetTime((float)transition->GetDuration() / (float)PR_MSEC_PER_SEC);
   } while (++i < display->mTransitionDurationCount);
 
   return valueList;
 }
@@ -5225,17 +5225,17 @@ nsComputedDOMStyle::DoGetTransitionPrope
   const nsStyleDisplay* display = StyleDisplay();
 
   nsDOMCSSValueList *valueList = GetROCSSValueList(true);
 
   NS_ABORT_IF_FALSE(display->mTransitionPropertyCount > 0,
                     "first item must be explicit");
   uint32_t i = 0;
   do {
-    const nsTransition *transition = &display->mTransitions[i];
+    const StyleTransition *transition = &display->mTransitions[i];
     nsROCSSPrimitiveValue* property = new nsROCSSPrimitiveValue;
     valueList->AppendCSSValue(property);
     nsCSSProperty cssprop = transition->GetProperty();
     if (cssprop == eCSSPropertyExtra_all_properties)
       property->SetIdent(eCSSKeyword_all);
     else if (cssprop == eCSSPropertyExtra_no_properties)
       property->SetIdent(eCSSKeyword_none);
     else if (cssprop == eCSSProperty_UNKNOWN)

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -4819,17 +4819,17 @@ nsRuleNode::ComputeDisplayData(void* aSt
     const TransitionPropInfo& i = transitionPropInfo[p];
     TransitionPropData& d = transitionPropData[p];
 
     display->*(i.sdCount) = d.num;
   }
 
   // Fill in the transitions we just allocated with the appropriate values.
   for (uint32_t i = 0; i < numTransitions; ++i) {
-    nsTransition *transition = &display->mTransitions[i];
+    StyleTransition *transition = &display->mTransitions[i];
 
     if (i >= delay.num) {
       transition->SetDelay(display->mTransitions[i % delay.num].GetDelay());
     } else if (delay.unit == eCSSUnit_Inherit) {
       // FIXME (Bug 522599) (for all transition properties): write a test that
       // detects when this was wrong for i >= delay.num if parent had
       // count for this property not equal to length
       NS_ABORT_IF_FALSE(i < parentDisplay->mTransitionDelayCount,

--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -2309,34 +2309,36 @@ void nsTimingFunction::AssignFromKeyword
   NS_ABORT_IF_FALSE(0 <= aTimingFunctionType && aTimingFunctionType < 5,
                     "keyword out of range");
   mFunc.mX1 = timingFunctionValues[aTimingFunctionType][0];
   mFunc.mY1 = timingFunctionValues[aTimingFunctionType][1];
   mFunc.mX2 = timingFunctionValues[aTimingFunctionType][2];
   mFunc.mY2 = timingFunctionValues[aTimingFunctionType][3];
 }
 
-nsTransition::nsTransition(const nsTransition& aCopy)
+mozilla::StyleTransition::StyleTransition(const StyleTransition& aCopy)
   : mTimingFunction(aCopy.mTimingFunction)
   , mDuration(aCopy.mDuration)
   , mDelay(aCopy.mDelay)
   , mProperty(aCopy.mProperty)
   , mUnknownProperty(aCopy.mUnknownProperty)
 {
 }
 
-void nsTransition::SetInitialValues()
+void
+mozilla::StyleTransition::SetInitialValues()
 {
   mTimingFunction = nsTimingFunction(NS_STYLE_TRANSITION_TIMING_FUNCTION_EASE);
   mDuration = 0.0;
   mDelay = 0.0;
   mProperty = eCSSPropertyExtra_all_properties;
 }
 
-void nsTransition::SetUnknownProperty(const nsAString& aUnknownProperty)
+void
+mozilla::StyleTransition::SetUnknownProperty(const nsAString& aUnknownProperty)
 {
   NS_ASSERTION(nsCSSProps::LookupProperty(aUnknownProperty,
                                           nsCSSProps::eEnabledForAllContent) ==
                  eCSSProperty_UNKNOWN,
                "should be unknown property");
   mProperty = eCSSProperty_UNKNOWN;
   mUnknownProperty = do_GetAtom(aUnknownProperty);
 }

--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -1804,19 +1804,21 @@ struct nsTimingFunction {
   {
     return !(*this == aOther);
   }
 
 private:
   void AssignFromKeyword(int32_t aTimingFunctionType);
 };
 
-struct nsTransition {
-  nsTransition() { /* leaves uninitialized; see also SetInitialValues */ }
-  explicit nsTransition(const nsTransition& aCopy);
+namespace mozilla {
+
+struct StyleTransition {
+  StyleTransition() { /* leaves uninitialized; see also SetInitialValues */ }
+  explicit StyleTransition(const StyleTransition& aCopy);
 
   void SetInitialValues();
 
   // Delay and Duration are in milliseconds
 
   const nsTimingFunction& GetTimingFunction() const { return mTimingFunction; }
   float GetDelay() const { return mDelay; }
   float GetDuration() const { return mDuration; }
@@ -1828,35 +1830,33 @@ struct nsTransition {
   void SetDelay(float aDelay) { mDelay = aDelay; }
   void SetDuration(float aDuration) { mDuration = aDuration; }
   void SetProperty(nsCSSProperty aProperty)
     {
       NS_ASSERTION(aProperty != eCSSProperty_UNKNOWN, "invalid property");
       mProperty = aProperty;
     }
   void SetUnknownProperty(const nsAString& aUnknownProperty);
-  void CopyPropertyFrom(const nsTransition& aOther)
+  void CopyPropertyFrom(const StyleTransition& aOther)
     {
       mProperty = aOther.mProperty;
       mUnknownProperty = aOther.mUnknownProperty;
     }
 
   nsTimingFunction& TimingFunctionSlot() { return mTimingFunction; }
 
 private:
   nsTimingFunction mTimingFunction;
   float mDuration;
   float mDelay;
   nsCSSProperty mProperty;
   nsCOMPtr<nsIAtom> mUnknownProperty; // used when mProperty is
                                       // eCSSProperty_UNKNOWN
 };
 
-namespace mozilla {
-
 struct StyleAnimation {
   StyleAnimation() { /* leaves uninitialized; see also SetInitialValues */ }
   explicit StyleAnimation(const StyleAnimation& aCopy);
 
   void SetInitialValues();
 
   // Delay and Duration are in milliseconds
 
@@ -1967,17 +1967,17 @@ struct nsStyleDisplay {
   // null, as appropriate.)
   uint8_t mBackfaceVisibility;
   uint8_t mTransformStyle;
   nsRefPtr<nsCSSValueSharedList> mSpecifiedTransform; // [reset]
   nsStyleCoord mTransformOrigin[3]; // [reset] percent, coord, calc, 3rd param is coord, calc only
   nsStyleCoord mChildPerspective; // [reset] coord
   nsStyleCoord mPerspectiveOrigin[2]; // [reset] percent, coord, calc
 
-  nsAutoTArray<nsTransition, 1> mTransitions; // [reset]
+  nsAutoTArray<mozilla::StyleTransition, 1> mTransitions; // [reset]
   // The number of elements in mTransitions that are not from repeating
   // a list due to another property being longer.
   uint32_t mTransitionTimingFunctionCount,
            mTransitionDurationCount,
            mTransitionDelayCount,
            mTransitionPropertyCount;
 
   nsAutoTArray<mozilla::StyleAnimation, 1> mAnimations; // [reset]

--- a/layout/style/nsTransitionManager.cpp
+++ b/layout/style/nsTransitionManager.cpp
@@ -224,17 +224,17 @@ nsTransitionManager::StyleContextChanged
 
   // Per http://lists.w3.org/Archives/Public/www-style/2009Aug/0109.html
   // I'll consider only the transitions from the number of items in
   // 'transition-property' on down, and later ones will override earlier
   // ones (tracked using |whichStarted|).
   bool startedAny = false;
   nsCSSPropertySet whichStarted;
   for (uint32_t i = disp->mTransitionPropertyCount; i-- != 0; ) {
-    const nsTransition& t = disp->mTransitions[i];
+    const StyleTransition& t = disp->mTransitions[i];
     // Check delay and duration first, since they default to zero, and
     // when they're both zero, we can ignore the transition.
     if (t.GetDelay() != 0.0f || t.GetDuration() != 0.0f) {
       // We might have something to transition.  See if any of the
       // properties in question changed and are animatable.
       // FIXME: Would be good to find a way to share code between this
       // interpretation of transition-property and the one below.
       nsCSSProperty property = t.GetProperty();
@@ -270,17 +270,17 @@ nsTransitionManager::StyleContextChanged
   // still in the set of properties to transition), but we didn't just
   // start the transition because delay and duration are both zero.
   if (et) {
     bool checkProperties =
       disp->mTransitions[0].GetProperty() != eCSSPropertyExtra_all_properties;
     nsCSSPropertySet allTransitionProperties;
     if (checkProperties) {
       for (uint32_t i = disp->mTransitionPropertyCount; i-- != 0; ) {
-        const nsTransition& t = disp->mTransitions[i];
+        const StyleTransition& t = disp->mTransitions[i];
         // FIXME: Would be good to find a way to share code between this
         // interpretation of transition-property and the one above.
         nsCSSProperty property = t.GetProperty();
         if (property == eCSSPropertyExtra_no_properties ||
             property == eCSSPropertyExtra_variable ||
             property == eCSSProperty_UNKNOWN) {
           // Nothing to do, but need to exclude this from cases below.
         } else if (property == eCSSPropertyExtra_all_properties) {
@@ -371,24 +371,25 @@ nsTransitionManager::StyleContextChanged
   }
 
   et->mStyleRule = nullptr;
 
   return coverRule.forget();
 }
 
 void
-nsTransitionManager::ConsiderStartingTransition(nsCSSProperty aProperty,
-                                                const nsTransition& aTransition,
-                                                dom::Element* aElement,
-                                                CommonElementAnimationData*& aElementTransitions,
-                                                nsStyleContext* aOldStyleContext,
-                                                nsStyleContext* aNewStyleContext,
-                                                bool* aStartedAny,
-                                                nsCSSPropertySet* aWhichStarted)
+nsTransitionManager::ConsiderStartingTransition(
+  nsCSSProperty aProperty,
+  const StyleTransition& aTransition,
+  dom::Element* aElement,
+  CommonElementAnimationData*& aElementTransitions,
+  nsStyleContext* aOldStyleContext,
+  nsStyleContext* aNewStyleContext,
+  bool* aStartedAny,
+  nsCSSPropertySet* aWhichStarted)
 {
   // IsShorthand itself will assert if aProperty is not a property.
   NS_ABORT_IF_FALSE(!nsCSSProps::IsShorthand(aProperty),
                     "property out of range");
   NS_ASSERTION(!aElementTransitions ||
                aElementTransitions->mElement == aElement, "Element mismatch");
 
   if (aWhichStarted->HasProperty(aProperty)) {

--- a/layout/style/nsTransitionManager.h
+++ b/layout/style/nsTransitionManager.h
@@ -11,19 +11,22 @@
 #include "mozilla/Attributes.h"
 #include "mozilla/MemoryReporting.h"
 #include "AnimationCommon.h"
 #include "nsCSSPseudoElements.h"
 
 class nsStyleContext;
 class nsPresContext;
 class nsCSSPropertySet;
-struct nsTransition;
 struct ElementDependentRuleProcessorData;
 
+namespace mozilla {
+struct StyleTransition;
+}
+
 /*****************************************************************************
  * Per-Element data                                                          *
  *****************************************************************************/
 
 struct ElementPropertyTransition : public mozilla::ElementAnimation
 {
   virtual ElementPropertyTransition* AsTransition() { return this; }
   virtual const ElementPropertyTransition* AsTransition() const { return this; }
@@ -151,17 +154,17 @@ public:
     bool aCreateIfNeeded);
 
 protected:
   virtual void ElementDataRemoved() MOZ_OVERRIDE;
   virtual void AddElementData(mozilla::css::CommonElementAnimationData* aData) MOZ_OVERRIDE;
 
 private:
   void ConsiderStartingTransition(nsCSSProperty aProperty,
-                                  const nsTransition& aTransition,
+                                  const mozilla::StyleTransition& aTransition,
                                   mozilla::dom::Element* aElement,
                                   CommonElementAnimationData*& aElementTransitions,
                                   nsStyleContext* aOldStyleContext,
                                   nsStyleContext* aNewStyleContext,
                                   bool* aStartedAny,
                                   nsCSSPropertySet* aWhichStarted);
   void WalkTransitionRule(ElementDependentRuleProcessorData* aData,
                           nsCSSPseudoElements::Type aPseudoType);