Make 'mapleader' an option and fix the help fragment scrolling issue.

common/content/help.js

@@ -8,8 +8,13 @@ function checkFragment() {
     document.title = document.getElementsByTagNameNS("http://www.w3.org/1999/xhtml", "title")[0].textContent;
     var frag = document.location.hash.substr(1);
     var elem = document.getElementById(frag);
-    if (elem)
+    function action() {
         window.content.scrollTo(0, window.content.scrollY + elem.getBoundingClientRect().top - 10); // 10px context
+    }
+    if (elem) {
+        action();
+        setTimeout(action, 10);
+    }
 }
 
 document.addEventListener("load", checkFragment, true);