At least at my company none of the Intranet pages seem to work well. Using Firefox, I constantly get password challenges during page loads, so many that I sometimes have to force the program to quite using the task manager. It seems that Internet Explorer passes all of my domain login information directly through to our Windows-powered servers, providing me direct access to in-company resources, while Mozilla does not (can not?) pass that same information through.
For me it's not that big of a deal to use the Mozilla-based browser for non-Intranet sites and Internet Explorer solely for Intranet sites, but I don't know how user friendly that is for the general population. I am not to proud to admit that I have navigated out of the Intranet and onto the Internet on Internet Explorer, but I am not really doing anything sensitive that involves the use of passwords or sensitive information on Internet Explorer anymore.