Get rid of nested functions declarations that are not on top level (causes strict mode warnings)

lib/ui.js

Index: lib/ui.js
===================================================================
--- a/lib/ui.js
+++ b/lib/ui.js
@@ -1711,28 +1711,28 @@ let UI = exports.UI =
       let data = RequestNotifier.getDataForNode(wnd.frameElement, true);
       if (data && !data[1].filter)
         addMenuItem(data);
     }
 
     // Look for a background image
     if (!hadImage)
     {
-      function extractImageURL(computedStyle, property)
+      let extractImageURL = function(computedStyle, property)
       {
         let value = computedStyle.getPropertyCSSValue(property);
         // CSSValueList
         if ("length" in value && value.length >= 1)
           value = value[0];
         // CSSValuePrimitiveType
         if ("primitiveType" in value && value.primitiveType == value.CSS_URI)
           return Utils.unwrapURL(value.getStringValue()).spec;
 
         return null;
-      }
+      };
 
       let node = target;
       while (node)
       {
         if (node.nodeType == Ci.nsIDOMNode.ELEMENT_NODE)
         {
           let style = wnd.getComputedStyle(node, "");
           let bgImage = extractImageURL(style, "background-image") || extractImageURL(style, "list-style-image");