That's a problem with the web access function. A while ago I started taking Firefox portable to work with me and I observed that the functionality of the online program was fairly limited on the browser. This is the case with a lot of company applications which run within a web browser.

The only solution, sadly, is to use IE's "Trident" engine for the application. You can make this possible in Firefox through this add-on though which may be of interest to you.