--- a/layout/style/nsDOMCSSDeclaration.cpp
+++ b/layout/style/nsDOMCSSDeclaration.cpp
@@ -249,16 +249,20 @@ nsDOMCSSDeclaration::SetProperty(const n
 }
 
 NS_IMETHODIMP
 nsDOMCSSDeclaration::RemoveProperty(const nsAString& aPropertyName,
                                     nsAString& aReturn)
 {
   nsresult rv = GetPropertyValue(aPropertyName, aReturn);
   NS_ENSURE_SUCCESS(rv, rv);
+  // If the property doesn't exist, it makes no sense to go further.
+  if (aReturn.IsEmpty()) {
+    return NS_OK;
+  }
   return RemovePropertyInternal(aPropertyName);
 }
 
 /* static */ void
 nsDOMCSSDeclaration::GetCSSParsingEnvironmentForRule(css::Rule* aRule,
                                                      CSSParsingEnvironment& aCSSParseEnv)
 {
   StyleSheet* sheet = aRule ? aRule->GetStyleSheet() : nullptr;