Bug 1112700 - Fix assertion failure: aPropID != eCSSPropertyExtra_variable r=me

layout/inspector/inDOMUtils.cpp

@@ -867,6 +867,11 @@ inDOMUtils::CssPropertyIsValid(const nsAString& aPropertyName,
     return NS_OK;
   }
 
+  if (propertyID == eCSSPropertyExtra_variable) {
+    *_retval = true;
+    return NS_OK;
+  }
+
   // Get a parser, parse the property.
   nsCSSParser parser;
   *_retval = parser.IsValueValidForProperty(propertyID, aPropertyValue);

layout/inspector/tests/test_css_property_is_valid.html

@@ -74,6 +74,11 @@
       property: "content",
       value: "\"hello\"",
       expected: true
+    },
+    {
+      property: "color",
+      value: "var(--some-kind-of-green)",
+      expected: true
     }
   ];