That part has always been kind of buggy. I have never tested it with different browsers though. I almost always use Internet Explorer and some times it works and some times not. I notice when things are not working correctly you get strange urls in the address bar.
Example: my newsletter section doesnt work and in the address bar I have:
http://www.insanediscounts.com/admin/mm_index.php?mod=e01
The last part =e01 shouldnt be visible
so look for stuff like that on parts that dont work correctly. Ofcourse the file e01 is encoded so you cant diagnose it past that. Thats been our problem the entire time that these numbers appear on parts not working. They gave us new copies of those files for the first 3 months but apparently there is some kind of bug in the encoding that breaks the script.
Maybe I just got a bad script or something.
I really like the software when it works though.
On the plus side, I have almost completed my newsletter mod. It is currently connecting to the x-cart database and getting the newsletter subscription emails and sending in html. I should finish it soon and then decide what to add next.
Anyway , sounds like its working pretty good for you for the most part besides the minor cart thing which is no big deal since you can get it to work in another browser.