--- a/layout/style/GenericSpecifiedValuesInlines.h
+++ b/layout/style/GenericSpecifiedValuesInlines.h
@@ -32,32 +32,36 @@ void
 GenericSpecifiedValues::SetIdentStringValue(nsCSSPropertyID aId, const nsString& aValue)
 {
   MOZ_STYLO_FORWARD(SetIdentStringValue, (aId, aValue))
 }
 
 void
 GenericSpecifiedValues::SetIdentStringValueIfUnset(nsCSSPropertyID aId, const nsString& aValue)
 {
-  MOZ_STYLO_FORWARD(SetIdentStringValueIfUnset, (aId, aValue))
-}
-
-void
-GenericSpecifiedValues::SetIdentAtomValueIfUnset(nsCSSPropertyID aId, nsIAtom* aValue)
-{
-  MOZ_STYLO_FORWARD(SetIdentAtomValueIfUnset, (aId, aValue))
+  if (!PropertyIsSet(aId)) {
+    SetIdentStringValue(aId, aValue);
+  }
 }
 
 void
 GenericSpecifiedValues::SetIdentAtomValue(nsCSSPropertyID aId, nsIAtom* aValue)
 {
   MOZ_STYLO_FORWARD(SetIdentAtomValue, (aId, aValue))
 }
 
 void
+GenericSpecifiedValues::SetIdentAtomValueIfUnset(nsCSSPropertyID aId, nsIAtom* aValue)
+{
+  if (!PropertyIsSet(aId)) {
+    SetIdentAtomValue(aId, aValue);
+  }
+}
+
+void
 GenericSpecifiedValues::SetKeywordValue(nsCSSPropertyID aId, int32_t aValue)
 {
   // there are some static asserts in MOZ_STYLO_FORWARD which
   // won't work with the overloaded SetKeywordValue function,
   // so we copy its expansion and use SetIntValue for decltype
   // instead
   static_assert(!mozilla::IsSame<decltype(&MOZ_STYLO_THIS_TYPE::SetIntValue),
                  decltype(&MOZ_STYLO_GECKO_TYPE::SetKeywordValue)>
@@ -70,31 +74,19 @@ GenericSpecifiedValues::SetKeywordValue(
     return AsServo()->SetKeywordValue(aId, aValue);
   }
   return AsGecko()->SetKeywordValue(aId, aValue);
 }
 
 void
 GenericSpecifiedValues::SetKeywordValueIfUnset(nsCSSPropertyID aId, int32_t aValue)
 {
-  // there are some static asserts in MOZ_STYLO_FORWARD which
-  // won't work with the overloaded SetKeywordValue function,
-  // so we copy its expansion and use SetIntValue for decltype
-  // instead
-  static_assert(!mozilla::IsSame<decltype(&MOZ_STYLO_THIS_TYPE::SetIntValue),
-                 decltype(&MOZ_STYLO_GECKO_TYPE::SetKeywordValueIfUnset)>
-        ::value, "Gecko subclass should define its own SetKeywordValueIfUnset");
-  static_assert(!mozilla::IsSame<decltype(&MOZ_STYLO_THIS_TYPE::SetIntValue),
-                 decltype(&MOZ_STYLO_SERVO_TYPE::SetKeywordValueIfUnset)>
-        ::value, "Servo subclass should define its own SetKeywordValueIfUnset");
-
-  if (IsServo()) {
-    return AsServo()->SetKeywordValueIfUnset(aId, aValue);
+  if (!PropertyIsSet(aId)) {
+    SetKeywordValue(aId, aValue);
   }
-  return AsGecko()->SetKeywordValueIfUnset(aId, aValue);
 }
 
 void
 GenericSpecifiedValues::SetIntValue(nsCSSPropertyID aId, int32_t aValue)
 {
   MOZ_STYLO_FORWARD(SetIntValue, (aId, aValue))
 }
 
@@ -102,17 +94,19 @@ void
 GenericSpecifiedValues::SetPixelValue(nsCSSPropertyID aId, float aValue)
 {
   MOZ_STYLO_FORWARD(SetPixelValue, (aId, aValue))
 }
 
 void
 GenericSpecifiedValues::SetPixelValueIfUnset(nsCSSPropertyID aId, float aValue)
 {
-  MOZ_STYLO_FORWARD(SetPixelValueIfUnset, (aId, aValue))
+  if (!PropertyIsSet(aId)) {
+    SetPixelValue(aId, aValue);
+  }
 }
 
 void
 GenericSpecifiedValues::SetLengthValue(nsCSSPropertyID aId, nsCSSValue aValue)
 {
   MOZ_STYLO_FORWARD(SetLengthValue, (aId, aValue))
 }
 
@@ -126,53 +120,61 @@ void
 GenericSpecifiedValues::SetPercentValue(nsCSSPropertyID aId, float aValue)
 {
   MOZ_STYLO_FORWARD(SetPercentValue, (aId, aValue))
 }
 
 void
 GenericSpecifiedValues::SetPercentValueIfUnset(nsCSSPropertyID aId, float aValue)
 {
-  MOZ_STYLO_FORWARD(SetPercentValueIfUnset, (aId, aValue))
+  if (!PropertyIsSet(aId)) {
+    SetPercentValue(aId, aValue);
+  }
 }
 
 void
 GenericSpecifiedValues::SetAutoValue(nsCSSPropertyID aId)
 {
   MOZ_STYLO_FORWARD(SetAutoValue, (aId))
 }
 
 void
 GenericSpecifiedValues::SetAutoValueIfUnset(nsCSSPropertyID aId)
 {
-  MOZ_STYLO_FORWARD(SetAutoValueIfUnset, (aId))
+  if (!PropertyIsSet(aId)) {
+    SetAutoValue(aId);
+  }
 }
 
 void
 GenericSpecifiedValues::SetCurrentColor(nsCSSPropertyID aId)
 {
   MOZ_STYLO_FORWARD(SetCurrentColor, (aId))
 }
 
 void
 GenericSpecifiedValues::SetCurrentColorIfUnset(nsCSSPropertyID aId)
 {
-  MOZ_STYLO_FORWARD(SetCurrentColorIfUnset, (aId))
+  if (!PropertyIsSet(aId)) {
+    SetCurrentColor(aId);
+  }
 }
 
 void
 GenericSpecifiedValues::SetColorValue(nsCSSPropertyID aId, nscolor aValue)
 {
   MOZ_STYLO_FORWARD(SetColorValue, (aId, aValue))
 }
 
 void
 GenericSpecifiedValues::SetColorValueIfUnset(nsCSSPropertyID aId, nscolor aValue)
 {
-  MOZ_STYLO_FORWARD(SetColorValueIfUnset, (aId, aValue))
+  if (!PropertyIsSet(aId)) {
+    SetColorValue(aId, aValue);
+  }
 }
 
 void
 GenericSpecifiedValues::SetFontFamily(const nsString& aValue)
 {
   MOZ_STYLO_FORWARD(SetFontFamily, (aValue))
 }
 

--- a/layout/style/ServoSpecifiedValues.h
+++ b/layout/style/ServoSpecifiedValues.h
@@ -23,90 +23,36 @@ public:
 
   ServoSpecifiedValues(nsPresContext* aContext, RawServoDeclarationBlock* aDecl);
 
   // GenericSpecifiedValues overrides
   bool PropertyIsSet(nsCSSPropertyID aId);
 
   void SetIdentStringValue(nsCSSPropertyID aId, const nsString& aValue);
 
-  void SetIdentStringValueIfUnset(nsCSSPropertyID aId, const nsString& aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetIdentStringValue(aId, aValue);
-    }
-  }
-
   void SetIdentAtomValue(nsCSSPropertyID aId, nsIAtom* aValue);
 
-  void SetIdentAtomValueIfUnset(nsCSSPropertyID aId, nsIAtom* aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetIdentAtomValue(aId, aValue);
-    }
-  }
-
   void SetKeywordValue(nsCSSPropertyID aId, int32_t aValue);
 
-  void SetKeywordValueIfUnset(nsCSSPropertyID aId, int32_t aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetKeywordValue(aId, aValue);
-    }
-  }
-
   void SetIntValue(nsCSSPropertyID aId, int32_t aValue);
 
   void SetPixelValue(nsCSSPropertyID aId, float aValue);
 
-  void SetPixelValueIfUnset(nsCSSPropertyID aId, float aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetPixelValue(aId, aValue);
-    }
-  }
-
   void SetLengthValue(nsCSSPropertyID aId, nsCSSValue aValue);
 
   void SetNumberValue(nsCSSPropertyID aId, float aValue);
 
   void SetPercentValue(nsCSSPropertyID aId, float aValue);
 
   void SetAutoValue(nsCSSPropertyID aId);
 
-  void SetAutoValueIfUnset(nsCSSPropertyID aId) {
-    if (!PropertyIsSet(aId)) {
-      SetAutoValue(aId);
-    }
-  }
-
-  void SetPercentValueIfUnset(nsCSSPropertyID aId, float aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetPercentValue(aId, aValue);
-    }
-  }
-
   void SetCurrentColor(nsCSSPropertyID aId);
 
-  void SetCurrentColorIfUnset(nsCSSPropertyID aId) {
-    if (!PropertyIsSet(aId)) {
-      SetCurrentColor(aId);
-    }
-  }
-
   void SetColorValue(nsCSSPropertyID aId, nscolor aValue);
 
-  void SetColorValueIfUnset(nsCSSPropertyID aId, nscolor aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetColorValue(aId, aValue);
-    }
-  }
-
   void SetFontFamily(const nsString& aValue);
   void SetTextDecorationColorOverride();
   void SetBackgroundImage(nsAttrValue& aValue);
 
 private:
   RefPtr<RawServoDeclarationBlock> mDecl;
 };
 

--- a/layout/style/nsRuleData.h
+++ b/layout/style/nsRuleData.h
@@ -124,65 +124,37 @@ struct nsRuleData final: mozilla::Generi
     return ValueFor(aId)->GetUnit() != eCSSUnit_Null;
   }
 
   void SetIdentStringValue(nsCSSPropertyID aId, const nsString& aValue)
   {
     ValueFor(aId)->SetStringValue(aValue, eCSSUnit_Ident);
   }
 
-  void SetIdentStringValueIfUnset(nsCSSPropertyID aId, const nsString& aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetIdentStringValue(aId, aValue);
-    }
-  }
-
   void SetIdentAtomValue(nsCSSPropertyID aId, nsIAtom* aValue)
   {
     nsCOMPtr<nsIAtom> atom = aValue;
     ValueFor(aId)->SetAtomIdentValue(atom.forget());
   }
 
-  void SetIdentAtomValueIfUnset(nsCSSPropertyID aId, nsIAtom* aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetIdentAtomValue(aId, aValue);
-    }
-  }
-
   void SetKeywordValue(nsCSSPropertyID aId, int32_t aValue)
   {
     ValueFor(aId)->SetIntValue(aValue, eCSSUnit_Enumerated);
   }
 
-  void SetKeywordValueIfUnset(nsCSSPropertyID aId, int32_t aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetKeywordValue(aId, aValue);
-    }
-  }
-
   void SetIntValue(nsCSSPropertyID aId, int32_t aValue)
   {
     ValueFor(aId)->SetIntValue(aValue, eCSSUnit_Integer);
   }
 
   void SetPixelValue(nsCSSPropertyID aId, float aValue)
   {
     ValueFor(aId)->SetFloatValue(aValue, eCSSUnit_Pixel);
   }
 
-  void SetPixelValueIfUnset(nsCSSPropertyID aId, float aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetPixelValue(aId, aValue);
-    }
-  }
-
   void SetLengthValue(nsCSSPropertyID aId, nsCSSValue aValue)
   {
     nsCSSValue* val = ValueFor(aId);
     *val = aValue;
   }
 
   void SetNumberValue(nsCSSPropertyID aId, float aValue)
   {
@@ -193,51 +165,25 @@ struct nsRuleData final: mozilla::Generi
   {
     ValueFor(aId)->SetPercentValue(aValue);
   }
 
   void SetAutoValue(nsCSSPropertyID aId) {
     ValueFor(aId)->SetAutoValue();
   }
 
-  void SetAutoValueIfUnset(nsCSSPropertyID aId) {
-    if (!PropertyIsSet(aId)) {
-      SetAutoValue(aId);
-    }
-  }
-
-  void SetPercentValueIfUnset(nsCSSPropertyID aId, float aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetPercentValue(aId, aValue);
-    }
-  }
-
   void SetCurrentColor(nsCSSPropertyID aId) {
     ValueFor(aId)->SetIntValue(NS_COLOR_CURRENTCOLOR, eCSSUnit_EnumColor);
   }
 
-  void SetCurrentColorIfUnset(nsCSSPropertyID aId) {
-    if (!PropertyIsSet(aId)) {
-      SetCurrentColor(aId);
-    }
-  }
-
   void SetColorValue(nsCSSPropertyID aId, nscolor aValue)
   {
     ValueFor(aId)->SetColorValue(aValue);
   }
 
-  void SetColorValueIfUnset(nsCSSPropertyID aId, nscolor aValue)
-  {
-    if (!PropertyIsSet(aId)) {
-      SetColorValue(aId, aValue);
-    }
-  }
-
   void SetFontFamily(const nsString& aValue);
   void SetTextDecorationColorOverride();
   void SetBackgroundImage(nsAttrValue& aValue);
 
 private:
   inline size_t GetPoisonOffset();
 
 };