Honour preventDefault() on modified link clicks b=319554 r+sr=jag

suite/common/contentAreaClick.js

@@ -170,7 +170,7 @@
   // should always return true for click to go through
   function contentAreaClick(event) 
   {
-    if (!event.isTrusted) {
+    if (!event.isTrusted || event.getPreventDefault()) {
       return true;
     }
 
@@ -193,7 +193,6 @@
     }
 
     if (pref && !isKeyPress && event.button == 1 &&
-        !event.getPreventDefault() &&
         pref.getBoolPref("middlemouse.contentLoadURL")) {
       if (middleMousePaste(event)) {
         event.stopPropagation();