Looks like the next version of SharePoint won't support FireFox fully.

as Jeff mentiones:

"Every time Microsoft is doing something cool (like Xbox 360 or Visual Studio Express), they do something that's crap like this"

Personally, I've used AvantBrowser for a long time, but am now working exclusively in FireFox (for the past few days, anyway). I'm not giving IE 7 a try until it becomes more stable, and I'm really loving the vast number of extensions for FireFox out there (IETab puts the final nail in the IE coffin for me now - even thought I don't even need it for most hebrew sites anymore - they seem to work perfect in FireFox!).

Here are the FireFox extensions I have installed:

• FasterFox  - to make it run faster
  
• TabMix Plus - much improved tab options
  
• FireBug (for debugging Javascript)
• MinimizeToTray - guess what it does