Mads created a GotDotNet workspace for tracking issues with SharePoint and non-IE browsers. I installed Firefox some time ago but but it aside since I didn't appear to do NTLM authentication which is needed for SharePoint access. One of the first posts in the form there is TIP: Use current Windows credentials in Firefox (warning: we are talking about GotDotNet so the link to the post may be unusable about 50% of the time while the GotDotNet crew does some “maintenance“). The tip explains how to enable NTLM in Firefox. However, it didn't work for me and after some googling I found this post which adds another setting to the mix but didn't solve the problem for me either. Turns out I had to add the server names to the bypass proxy list for it to work.
SharePoint seems to work except for ActiveX controls, which I see Mads already posted about. The most interesting thing to me though was checking out Reporting Services from Firefox which is pretty much unusable. Very ugly. I will have to look into seeing if I can make them work using the RsWebParts (which I'm still working on version 1.2 (parameters are a pain)).