diff --git a/content/smil/nsSMILAnimationFunction.cpp b/content/smil/nsSMILAnimationFunction.cpp
index 5611b17a9131..aad2ca3c2822 100644
--- a/content/smil/nsSMILAnimationFunction.cpp
+++ b/content/smil/nsSMILAnimationFunction.cpp
@@ -248,8 +248,7 @@ nsSMILAnimationFunction::ComposeResult(const nsISMILAttr& aSMILAttr,
   nsSMILValue result(aResult.mType);
 
   if (mSimpleDuration.IsIndefinite() ||
-      (HasAttr(nsGkAtoms::values) && values.Length() == 1)) {
-
+      (values.Length() == 1 && TreatSingleValueAsStatic())) {
     // Indefinite duration or only one value set: Always set the first value
     result = values[0];
 
diff --git a/content/smil/nsSMILAnimationFunction.h b/content/smil/nsSMILAnimationFunction.h
index 86ebcb207f9f..7f9db251fe33 100644
--- a/content/smil/nsSMILAnimationFunction.h
+++ b/content/smil/nsSMILAnimationFunction.h
@@ -327,6 +327,13 @@ protected:
   void     CheckKeyTimes(PRUint32 aNumValues);
   void     CheckKeySplines(PRUint32 aNumValues);
 
+  // When GetValues() returns a single-value array, this method indicates
+  // whether that single value can be understood to be a static value, to be
+  // set for the full animation duration.
+  virtual PRBool TreatSingleValueAsStatic() const {
+    return HasAttr(nsGkAtoms::values);
+  }
+
   inline PRBool IsToAnimation() const {
     return !HasAttr(nsGkAtoms::values) &&
             HasAttr(nsGkAtoms::to) &&
diff --git a/content/smil/nsSMILSetAnimationFunction.cpp b/content/smil/nsSMILSetAnimationFunction.cpp
index 71d56c728423..4efe1faa82e8 100644
--- a/content/smil/nsSMILSetAnimationFunction.cpp
+++ b/content/smil/nsSMILSetAnimationFunction.cpp
@@ -97,32 +97,6 @@ nsSMILSetAnimationFunction::UnsetAttr(nsIAtom* aAttribute)
   return nsSMILAnimationFunction::UnsetAttr(aAttribute);
 }
 
-nsresult
-nsSMILSetAnimationFunction::InterpolateResult(const nsSMILValueArray& aValues,
-                                              nsSMILValue& aResult,
-                                              nsSMILValue& aBaseValue)
-{
-  // Sanity Checks
-  const nsSMILTime& dur = mSimpleDuration.GetMillis();
-  NS_ABORT_IF_FALSE(mSampleTime >= 0.0f, "Sample time should not be negative");
-  NS_ABORT_IF_FALSE(dur >= 0.0f, "Simple duration should not be negative");
-  NS_ABORT_IF_FALSE(IsToAnimation(), "Set element only supports to-animation");
-
-  if (mSampleTime >= dur || mSampleTime < 0) {
-    NS_ERROR("Animation sampled outside interval");
-    return NS_ERROR_FAILURE;
-  }
-  if (aValues.Length() != 1) {
-    NS_ERROR("Unexpected number of values");
-    return NS_ERROR_FAILURE;
-  }
-  // End Sanity Checks
-
-  // Always use the 'to' value (which should be first & only elem in |aValues|)
-  aResult = aValues[0];
-  return NS_OK;
-}
-
 PRBool
 nsSMILSetAnimationFunction::HasAttr(nsIAtom* aAttName) const
 {
diff --git a/content/smil/nsSMILSetAnimationFunction.h b/content/smil/nsSMILSetAnimationFunction.h
index 49ad514ad2da..b06c8a7f60f4 100644
--- a/content/smil/nsSMILSetAnimationFunction.h
+++ b/content/smil/nsSMILSetAnimationFunction.h
@@ -71,17 +71,19 @@ public:
    * @returns PR_TRUE if aAttribute is a recognized animation-related
    *          attribute; PR_FALSE otherwise.
    */
-  virtual PRBool UnsetAttr(nsIAtom* aAttribute);
+  NS_OVERRIDE virtual PRBool UnsetAttr(nsIAtom* aAttribute);
 
 protected:
-  NS_OVERRIDE virtual nsresult
-    InterpolateResult(const nsSMILValueArray& aValues,
-                      nsSMILValue& aResult, nsSMILValue& aBaseValue);
-
-  virtual PRBool             HasAttr(nsIAtom* aAttName) const;
-  virtual const nsAttrValue* GetAttr(nsIAtom* aAttName) const;
-  virtual PRBool             GetAttr(nsIAtom* aAttName,
-                                     nsAString& aResult) const;
+  // <set> uses the "to" attribute as its only source of animation values
+  // (which gives us a single value in our values array), and we want to use
+  // that value whenever the animation is active (no interpolation or anything).
+  NS_OVERRIDE virtual PRBool TreatSingleValueAsStatic() const {
+    return PR_TRUE;
+  }
+  NS_OVERRIDE virtual PRBool             HasAttr(nsIAtom* aAttName) const;
+  NS_OVERRIDE virtual const nsAttrValue* GetAttr(nsIAtom* aAttName) const;
+  NS_OVERRIDE virtual PRBool             GetAttr(nsIAtom* aAttName,
+                                                 nsAString& aResult) const;
 
   PRBool IsDisallowedAttribute(const nsIAtom* aAttribute) const;
 };