Resets focus on last Maths element when closing popup windows.

unpacked/extensions/HelpDialog.js

@@ -181,6 +181,7 @@
         (this.id === 'MathJax_HelpClose' &&
          (event.keyCode === KEY.SPACE || event.keyCode === KEY.RETURN))) {
       HELP.Remove(event);
+      MENU.CurrentNode().focus();
       FALSE(event);
     }
   },

unpacked/extensions/MathMenu.js

@@ -1049,6 +1049,7 @@
         (this.id === 'MathJax_AboutClose' &&
          (event.keyCode === KEY.SPACE || event.keyCode === KEY.RETURN))) {
       MENU.About.Remove(event);
+      MENU.CurrentNode().focus();
       FALSE(event);
     }
   },