diff --git a/dom/animation/AnimValuesStyleRule.cpp b/dom/animation/AnimValuesStyleRule.cpp
index 4070950c5470..08b91453a4bb 100644
--- a/dom/animation/AnimValuesStyleRule.cpp
+++ b/dom/animation/AnimValuesStyleRule.cpp
@@ -56,6 +56,14 @@ AnimValuesStyleRule::MightMapInheritedStyleData()
   return mStyleBits & NS_STYLE_INHERITED_STRUCT_MASK;
 }
 
+bool
+AnimValuesStyleRule::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                                   nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 void
 AnimValuesStyleRule::List(FILE* out, int32_t aIndent) const
diff --git a/dom/animation/AnimValuesStyleRule.h b/dom/animation/AnimValuesStyleRule.h
index 97f7d4f5309a..8a4ee1f6dcdc 100644
--- a/dom/animation/AnimValuesStyleRule.h
+++ b/dom/animation/AnimValuesStyleRule.h
@@ -32,6 +32,8 @@ public:
   // nsIStyleRule implementation
   void MapRuleInfoInto(nsRuleData* aRuleData) override;
   bool MightMapInheritedStyleData() override;
+  bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                     nsCSSValue* aValue) override;
 #ifdef DEBUG
   void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
diff --git a/dom/base/nsMappedAttributes.cpp b/dom/base/nsMappedAttributes.cpp
index fb1943b248e3..52e8f4e91721 100644
--- a/dom/base/nsMappedAttributes.cpp
+++ b/dom/base/nsMappedAttributes.cpp
@@ -192,6 +192,14 @@ nsMappedAttributes::MightMapInheritedStyleData()
   return true;
 }
 
+/* virtual */ bool
+nsMappedAttributes::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                                  nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 nsMappedAttributes::List(FILE* out, int32_t aIndent) const
diff --git a/dom/base/nsMappedAttributes.h b/dom/base/nsMappedAttributes.h
index 45808281754e..30105c4d5ed0 100644
--- a/dom/base/nsMappedAttributes.h
+++ b/dom/base/nsMappedAttributes.h
@@ -75,6 +75,8 @@ public:
   // nsIStyleRule 
   virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
   virtual bool MightMapInheritedStyleData() override;
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) override;
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
diff --git a/dom/html/HTMLBodyElement.cpp b/dom/html/HTMLBodyElement.cpp
index 0a924074d24e..0c115f47b6be 100644
--- a/dom/html/HTMLBodyElement.cpp
+++ b/dom/html/HTMLBodyElement.cpp
@@ -174,6 +174,14 @@ BodyRule::MightMapInheritedStyleData()
   return false;
 }
 
+/* virtual */ bool
+BodyRule::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                        nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 BodyRule::List(FILE* out, int32_t aIndent) const
diff --git a/dom/html/HTMLBodyElement.h b/dom/html/HTMLBodyElement.h
index 5696ecfd142f..20e2acba7bae 100644
--- a/dom/html/HTMLBodyElement.h
+++ b/dom/html/HTMLBodyElement.h
@@ -29,6 +29,8 @@ public:
   // nsIStyleRule interface
   virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
   virtual bool MightMapInheritedStyleData() override;
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) override;
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
diff --git a/layout/style/Declaration.cpp b/layout/style/Declaration.cpp
index c6eea9d2ae15..f77921c14329 100644
--- a/layout/style/Declaration.cpp
+++ b/layout/style/Declaration.cpp
@@ -35,6 +35,14 @@ ImportantStyleData::MightMapInheritedStyleData()
   return Declaration()->MapsImportantInheritedStyleData();
 }
 
+/* virtual */ bool
+ImportantStyleData::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                                  nsCSSValue* aValue)
+{
+  return Declaration()->GetDiscretelyAnimatedCSSValue(aProperty, aValue);
+}
+
+
 #ifdef DEBUG
 /* virtual */ void
 ImportantStyleData::List(FILE* out, int32_t aIndent) const
@@ -111,6 +119,21 @@ Declaration::MightMapInheritedStyleData()
   return mData->HasInheritedStyleData();
 }
 
+/* virtual */ bool
+Declaration::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                           nsCSSValue* aValue)
+{
+  nsCSSCompressedDataBlock* data = GetValueIsImportant(aProperty)
+                                   ? mImportantData : mData;
+  const nsCSSValue* value = data->ValueFor(aProperty);
+  if (!value) {
+    return false;
+  }
+  *aValue = *value;
+  return true;
+}
+
+
 bool
 Declaration::MapsImportantInheritedStyleData() const
 {
diff --git a/layout/style/Declaration.h b/layout/style/Declaration.h
index 46561e406619..f1d444c45a81 100644
--- a/layout/style/Declaration.h
+++ b/layout/style/Declaration.h
@@ -60,6 +60,8 @@ public:
   // nsIStyleRule interface
   virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
   virtual bool MightMapInheritedStyleData() override;
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) override;
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
@@ -103,6 +105,8 @@ public:
   // nsIStyleRule implementation
   virtual void MapRuleInfoInto(nsRuleData *aRuleData) override;
   virtual bool MightMapInheritedStyleData() override;
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) override;
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
diff --git a/layout/style/StyleAnimationValue.cpp b/layout/style/StyleAnimationValue.cpp
index 430549cd0648..be062cc49a5d 100644
--- a/layout/style/StyleAnimationValue.cpp
+++ b/layout/style/StyleAnimationValue.cpp
@@ -499,6 +499,7 @@ StyleAnimationValue::ComputeDistance(nsCSSProperty aProperty,
     case eUnit_UnparsedString:
     case eUnit_URL:
     case eUnit_CurrentColor:
+    case eUnit_DiscreteCSSValue:
       return false;
 
     case eUnit_Enumerated:
@@ -2269,6 +2270,7 @@ StyleAnimationValue::AddWeighted(nsCSSProperty aProperty,
     case eUnit_UnparsedString:
     case eUnit_URL:
     case eUnit_CurrentColor:
+    case eUnit_DiscreteCSSValue:
       return false;
 
     case eUnit_Enumerated:
@@ -3061,14 +3063,16 @@ StyleAnimationValue::UncomputeValue(nsCSSProperty aProperty,
       break;
     case eUnit_Calc:
     case eUnit_ObjectPosition:
-    case eUnit_URL: {
+    case eUnit_URL:
+    case eUnit_DiscreteCSSValue: {
       nsCSSValue* val = aComputedValue.GetCSSValueValue();
       // Sanity-check that the underlying unit in the nsCSSValue is what we
       // expect for our StyleAnimationValue::Unit:
       MOZ_ASSERT((unit == eUnit_Calc && val->GetUnit() == eCSSUnit_Calc) ||
                  (unit == eUnit_ObjectPosition &&
                   val->GetUnit() == eCSSUnit_Array) ||
-                 (unit == eUnit_URL && val->GetUnit() == eCSSUnit_URL),
+                 (unit == eUnit_URL && val->GetUnit() == eCSSUnit_URL) ||
+                 unit == eUnit_DiscreteCSSValue,
                  "unexpected unit");
       aSpecifiedValue = *val;
       break;
@@ -3597,8 +3601,11 @@ StyleAnimationValue::ExtractComputedValue(nsCSSProperty aProperty,
     aStyleContext->StyleData(nsCSSProps::kSIDTable[aProperty]);
   ptrdiff_t ssOffset = nsCSSProps::kStyleStructOffsetTable[aProperty];
   nsStyleAnimType animType = nsCSSProps::kAnimTypeTable[aProperty];
-  MOZ_ASSERT(0 <= ssOffset || animType == eStyleAnimType_Custom,
-             "must be dealing with animatable property");
+  MOZ_ASSERT(0 <= ssOffset ||
+             animType == eStyleAnimType_Custom ||
+             animType == eStyleAnimType_Discrete,
+             "all animation types other than Custom and Discrete must " \
+             "specify a style struct offset to extract values from");
   switch (animType) {
     case eStyleAnimType_Custom:
       switch (aProperty) {
@@ -4213,6 +4220,14 @@ StyleAnimationValue::ExtractComputedValue(nsCSSProperty aProperty,
                                                   eUnit_Shadow);
       return true;
     }
+    case eStyleAnimType_Discrete: {
+      auto cssValue = MakeUnique<nsCSSValue>(eCSSUnit_Unset);
+      aStyleContext->RuleNode()->GetDiscretelyAnimatedCSSValue(aProperty,
+                                                               cssValue.get());
+      aComputedValue.SetAndAdoptCSSValueValue(cssValue.release(),
+                                              eUnit_DiscreteCSSValue);
+      return true;
+    }
     case eStyleAnimType_None:
       NS_NOTREACHED("shouldn't use on non-animatable properties");
   }
@@ -4318,6 +4333,7 @@ StyleAnimationValue::operator=(const StyleAnimationValue& aOther)
     case eUnit_Calc:
     case eUnit_ObjectPosition:
     case eUnit_URL:
+    case eUnit_DiscreteCSSValue:
       MOZ_ASSERT(IsCSSValueUnit(mUnit),
                  "This clause is for handling nsCSSValue-backed units");
       MOZ_ASSERT(aOther.mValue.mCSSValue, "values may not be null");
@@ -4595,6 +4611,7 @@ StyleAnimationValue::operator==(const StyleAnimationValue& aOther) const
     case eUnit_Calc:
     case eUnit_ObjectPosition:
     case eUnit_URL:
+    case eUnit_DiscreteCSSValue:
       MOZ_ASSERT(IsCSSValueUnit(mUnit),
                  "This clause is for handling nsCSSValue-backed units");
       return *mValue.mCSSValue == *aOther.mValue.mCSSValue;
diff --git a/layout/style/StyleAnimationValue.h b/layout/style/StyleAnimationValue.h
index 14509db454b4..bc29cb5db7cb 100644
--- a/layout/style/StyleAnimationValue.h
+++ b/layout/style/StyleAnimationValue.h
@@ -277,6 +277,7 @@ public:
     eUnit_ObjectPosition, // nsCSSValue* (never null), always with a
                           // 4-entry nsCSSValue::Array
     eUnit_URL, // nsCSSValue* (never null), always with a css::URLValue
+    eUnit_DiscreteCSSValue, // nsCSSValue* (never null)
     eUnit_CSSValuePair, // nsCSSValuePair* (never null)
     eUnit_CSSValueTriplet, // nsCSSValueTriplet* (never null)
     eUnit_CSSRect, // nsCSSRect* (never null)
@@ -477,7 +478,8 @@ private:
   static bool IsCSSValueUnit(Unit aUnit) {
     return aUnit == eUnit_Calc ||
            aUnit == eUnit_ObjectPosition ||
-           aUnit == eUnit_URL;
+           aUnit == eUnit_URL ||
+           aUnit == eUnit_DiscreteCSSValue;
   }
   static bool IsCSSValuePairUnit(Unit aUnit) {
     return aUnit == eUnit_CSSValuePair;
diff --git a/layout/style/nsCSSPropList.h b/layout/style/nsCSSPropList.h
index 5f80a6123c0b..26edead97568 100644
--- a/layout/style/nsCSSPropList.h
+++ b/layout/style/nsCSSPropList.h
@@ -334,7 +334,7 @@ CSS_PROP_POSITION(
     VARIANT_HK,
     kAutoCompletionAlignJustifyContent,
     CSS_PROP_NO_OFFSET,
-    eStyleAnimType_None)
+    eStyleAnimType_Discrete)
 CSS_PROP_POSITION(
     align-items,
     align_items,
@@ -344,7 +344,7 @@ CSS_PROP_POSITION(
     VARIANT_HK,
     kAutoCompletionAlignItems,
     CSS_PROP_NO_OFFSET,
-    eStyleAnimType_None)
+    eStyleAnimType_Discrete)
 CSS_PROP_POSITION(
     align-self,
     align_self,
@@ -354,7 +354,7 @@ CSS_PROP_POSITION(
     VARIANT_HK,
     kAutoCompletionAlignJustifySelf,
     CSS_PROP_NO_OFFSET,
-    eStyleAnimType_None)
+    eStyleAnimType_Discrete)
 CSS_PROP_SHORTHAND(
     all,
     all,
@@ -2358,7 +2358,7 @@ CSS_PROP_POSITION(
     VARIANT_HK,
     kAutoCompletionAlignJustifyContent,
     CSS_PROP_NO_OFFSET,
-    eStyleAnimType_None)
+    eStyleAnimType_Discrete)
 CSS_PROP_POSITION(
     justify-items,
     justify_items,
@@ -2369,7 +2369,7 @@ CSS_PROP_POSITION(
     // for auto-completion we use same values as justify-self:
     kAutoCompletionAlignJustifySelf,
     CSS_PROP_NO_OFFSET,
-    eStyleAnimType_None)
+    eStyleAnimType_Discrete)
 CSS_PROP_POSITION(
     justify-self,
     justify_self,
@@ -2379,7 +2379,7 @@ CSS_PROP_POSITION(
     VARIANT_HK,
     kAutoCompletionAlignJustifySelf,
     CSS_PROP_NO_OFFSET,
-    eStyleAnimType_None)
+    eStyleAnimType_Discrete)
 #ifndef CSS_PROP_LIST_ONLY_COMPONENTS_OF_ALL_SHORTHAND
 #ifndef CSS_PROP_LIST_EXCLUDE_INTERNAL
 CSS_PROP_FONT(
diff --git a/layout/style/nsCSSProps.h b/layout/style/nsCSSProps.h
index e5050f97af75..d8201d356746 100644
--- a/layout/style/nsCSSProps.h
+++ b/layout/style/nsCSSProps.h
@@ -326,6 +326,9 @@ enum nsStyleAnimType {
   // RefPtr<nsCSSShadowArray> values
   eStyleAnimType_Shadow,
 
+  // discrete values
+  eStyleAnimType_Discrete,
+
   // property not animatable
   eStyleAnimType_None
 };
diff --git a/layout/style/nsHTMLStyleSheet.cpp b/layout/style/nsHTMLStyleSheet.cpp
index 25f7d3224673..288d93384490 100644
--- a/layout/style/nsHTMLStyleSheet.cpp
+++ b/layout/style/nsHTMLStyleSheet.cpp
@@ -58,6 +58,14 @@ nsHTMLStyleSheet::HTMLColorRule::MightMapInheritedStyleData()
   return true;
 }
 
+/* virtual */ bool
+nsHTMLStyleSheet::HTMLColorRule::
+GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty, nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 nsHTMLStyleSheet::HTMLColorRule::List(FILE* out, int32_t aIndent) const
@@ -103,6 +111,14 @@ nsHTMLStyleSheet::TableTHRule::MightMapInheritedStyleData()
   return true;
 }
 
+/* virtual */ bool
+nsHTMLStyleSheet::TableTHRule::
+GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty, nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 /* virtual */ void
 nsHTMLStyleSheet::TableQuirkColorRule::MapRuleInfoInto(nsRuleData* aRuleData)
 {
@@ -122,6 +138,13 @@ nsHTMLStyleSheet::TableQuirkColorRule::MightMapInheritedStyleData()
   return true;
 }
 
+/* virtual */ bool
+nsHTMLStyleSheet::TableQuirkColorRule::
+GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty, nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
 
 NS_IMPL_ISUPPORTS(nsHTMLStyleSheet::LangRule, nsIStyleRule)
 
@@ -142,6 +165,14 @@ nsHTMLStyleSheet::LangRule::MightMapInheritedStyleData()
   return true;
 }
 
+/* virtual */ bool
+nsHTMLStyleSheet::LangRule::
+GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty, nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 nsHTMLStyleSheet::LangRule::List(FILE* out, int32_t aIndent) const
diff --git a/layout/style/nsHTMLStyleSheet.h b/layout/style/nsHTMLStyleSheet.h
index 62fddf160f4e..ed53483fe725 100644
--- a/layout/style/nsHTMLStyleSheet.h
+++ b/layout/style/nsHTMLStyleSheet.h
@@ -84,6 +84,8 @@ private:
     // nsIStyleRule interface
     virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
     virtual bool MightMapInheritedStyleData() override;
+    virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                               nsCSSValue* aValue) override;
   #ifdef DEBUG
     virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
   #endif
@@ -107,6 +109,8 @@ private:
     // nsIStyleRule interface
     virtual void MapRuleInfoInto(nsRuleData* aRuleData) override = 0;
     virtual bool MightMapInheritedStyleData() override = 0;
+    virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                               nsCSSValue* aValue) override = 0;
   #ifdef DEBUG
     virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
   #endif
@@ -121,6 +125,8 @@ private:
 
     virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
     virtual bool MightMapInheritedStyleData() override;
+    virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                               nsCSSValue* aValue) override;
   };
 
   // Rule to handle quirk table colors
@@ -130,6 +136,8 @@ private:
 
     virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
     virtual bool MightMapInheritedStyleData() override;
+    virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                               nsCSSValue* aValue) override;
   };
 
 public: // for mLangRuleTable structures only
@@ -149,6 +157,8 @@ public: // for mLangRuleTable structures only
     // nsIStyleRule interface
     virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
     virtual bool MightMapInheritedStyleData() override;
+    virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                               nsCSSValue* aValue) override;
   #ifdef DEBUG
     virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
   #endif
diff --git a/layout/style/nsIStyleRule.h b/layout/style/nsIStyleRule.h
index 9301728b4135..36c3d3ee19e1 100644
--- a/layout/style/nsIStyleRule.h
+++ b/layout/style/nsIStyleRule.h
@@ -13,8 +13,10 @@
 
 #include <stdio.h>
 
+#include "nsCSSProperty.h"
 #include "nsISupports.h"
 
+class nsCSSValue;
 struct nsRuleData;
 
 // IID for the nsIStyleRule interface {f75f3f70-435d-43a6-a01b-65970489ca26}
@@ -77,6 +79,13 @@ public:
    */
   virtual bool MightMapInheritedStyleData() = 0;
 
+  /**
+   * Gets and sets given aProperty's value to aValue.
+   * Returns true, if aValue is filled in this rule.
+   */
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) = 0;
+
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const = 0;
 #endif
diff --git a/layout/style/nsRuleNode.cpp b/layout/style/nsRuleNode.cpp
index 5f1ed453c9f8..b3be9dcd8187 100644
--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -10364,6 +10364,21 @@ nsRuleNode::GetStyleData(nsStyleStructID aSID,
   return data;
 }
 
+void
+nsRuleNode::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                          nsCSSValue* aValue)
+{
+  for (nsRuleNode* node = this; node; node = node->GetParent()) {
+    nsIStyleRule* rule = node->GetRule();
+    if (!rule) {
+      continue;
+    }
+    if (rule->GetDiscretelyAnimatedCSSValue(aProperty, aValue)) {
+      return;
+    }
+  }
+}
+
 /* static */ bool
 nsRuleNode::HasAuthorSpecifiedRules(nsStyleContext* aStyleContext,
                                     uint32_t ruleTypeMask,
diff --git a/layout/style/nsRuleNode.h b/layout/style/nsRuleNode.h
index 8c14cb08d3b9..6aea143af28b 100644
--- a/layout/style/nsRuleNode.h
+++ b/layout/style/nsRuleNode.h
@@ -861,6 +861,8 @@ public:
                            nsStyleContext* aContext,
                            bool aComputeData);
 
+  void GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                     nsCSSValue* aValue);
 
   // See comments in GetStyleData for an explanation of what the
   // code below does.
diff --git a/layout/style/nsStyleSet.cpp b/layout/style/nsStyleSet.cpp
index 3faa23ff898a..1d72d657e2c1 100644
--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -62,6 +62,14 @@ nsEmptyStyleRule::MightMapInheritedStyleData()
   return false;
 }
 
+/* virtual */ bool
+nsEmptyStyleRule::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                                nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 nsEmptyStyleRule::List(FILE* out, int32_t aIndent) const
@@ -121,6 +129,14 @@ nsInitialStyleRule::MightMapInheritedStyleData()
   return true;
 }
 
+/* virtual */ bool
+nsInitialStyleRule::GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                                  nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 nsInitialStyleRule::List(FILE* out, int32_t aIndent) const
@@ -152,6 +168,14 @@ nsDisableTextZoomStyleRule::MightMapInheritedStyleData()
   return true;
 }
 
+/* virtual */ bool
+nsDisableTextZoomStyleRule::
+GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty, nsCSSValue* aValue)
+{
+  MOZ_ASSERT(false, "GetDiscretelyAnimatedCSSValue is not implemented yet");
+  return false;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 nsDisableTextZoomStyleRule::List(FILE* out, int32_t aIndent) const
diff --git a/layout/style/nsStyleSet.h b/layout/style/nsStyleSet.h
index 8aed8c85ba59..a50d0e263880 100644
--- a/layout/style/nsStyleSet.h
+++ b/layout/style/nsStyleSet.h
@@ -52,6 +52,8 @@ public:
   NS_DECL_ISUPPORTS
   virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
   virtual bool MightMapInheritedStyleData() override;
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) override;
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
@@ -66,6 +68,8 @@ public:
   NS_DECL_ISUPPORTS
   virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
   virtual bool MightMapInheritedStyleData() override;
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) override;
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
@@ -80,6 +84,8 @@ public:
   NS_DECL_ISUPPORTS
   virtual void MapRuleInfoInto(nsRuleData* aRuleData) override;
   virtual bool MightMapInheritedStyleData() override;
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSProperty aProperty,
+                                             nsCSSValue* aValue) override;
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override;
 #endif
diff --git a/layout/style/nsTransitionManager.cpp b/layout/style/nsTransitionManager.cpp
index f1f30e8cde1b..69aaeeda55db 100644
--- a/layout/style/nsTransitionManager.cpp
+++ b/layout/style/nsTransitionManager.cpp
@@ -283,6 +283,17 @@ NS_IMPL_CYCLE_COLLECTION(nsTransitionManager, mEventDispatcher)
 NS_IMPL_CYCLE_COLLECTION_ROOT_NATIVE(nsTransitionManager, AddRef)
 NS_IMPL_CYCLE_COLLECTION_UNROOT_NATIVE(nsTransitionManager, Release)
 
+static inline bool
+ExtractNonDiscreteComputedValue(nsCSSProperty aProperty,
+                                nsStyleContext* aStyleContext,
+                                StyleAnimationValue& aComputedValue)
+{
+  return (nsCSSProps::kAnimTypeTable[aProperty] != eStyleAnimType_Discrete ||
+          aProperty == eCSSProperty_visibility) &&
+         StyleAnimationValue::ExtractComputedValue(aProperty, aStyleContext,
+                                                   aComputedValue);
+}
+
 void
 nsTransitionManager::StyleContextChanged(dom::Element *aElement,
                                          nsStyleContext *aOldStyleContext,
@@ -552,9 +563,8 @@ nsTransitionManager::UpdateTransitions(
           // duration are both zero, or because the new value is not
           // interpolable); a new transition would have anim->ToValue()
           // matching currentValue
-          !StyleAnimationValue::ExtractComputedValue(anim->TransitionProperty(),
-                                                     aNewStyleContext,
-                                                     currentValue) ||
+          !ExtractNonDiscreteComputedValue(anim->TransitionProperty(),
+                                           aNewStyleContext, currentValue) ||
           currentValue != anim->ToValue()) {
         // stop the transition
         if (anim->HasCurrentEffect()) {
@@ -619,12 +629,8 @@ nsTransitionManager::ConsiderStartingTransition(
 
   StyleAnimationValue startValue, endValue, dummyValue;
   bool haveValues =
-    StyleAnimationValue::ExtractComputedValue(aProperty,
-                                              aOldStyleContext,
-                                              startValue) &&
-    StyleAnimationValue::ExtractComputedValue(aProperty,
-                                              aNewStyleContext,
-                                              endValue);
+    ExtractNonDiscreteComputedValue(aProperty, aOldStyleContext, startValue) &&
+    ExtractNonDiscreteComputedValue(aProperty, aNewStyleContext, endValue);
 
   bool haveChange = startValue != endValue;
 
@@ -929,9 +935,8 @@ nsTransitionManager::PruneCompletedTransitions(mozilla::dom::Element* aElement,
     // Since effect is a finished transition, we know it didn't
     // influence style.
     StyleAnimationValue currentValue;
-    if (!StyleAnimationValue::ExtractComputedValue(anim->TransitionProperty(),
-                                                   aNewStyleContext,
-                                                   currentValue) ||
+    if (!ExtractNonDiscreteComputedValue(anim->TransitionProperty(),
+                                         aNewStyleContext, currentValue) ||
         currentValue != anim->ToValue()) {
       anim->CancelFromStyle();
       animations.RemoveElementAt(i);