Some browsers (FF and IE) prevent the focus behaviour because it's (was) abused for popup spam. It can be turned on through security settings but since it's off by default, the focus method is unreliable.
This is an old problem. Here is a discussion of the same problem from 2006!
http://bytes.com/topic/javascript/answers/482500-popup-focus-behaviour-moz-firefox-ie
A workaround is to close and reopen the window popup window for those browsers.
See here:
How to focus on JS popups in Firefox & IE?
PS. It is generally advised that you shouldn't refocus a popup window programmatically. If you need to do something like this, a popup is not likely the best choice for the task.