Updated on 2 computers - one XP and one Windows 7. Google Toolbar enabled caused "Open New Window" to not work anywhere near correctly. 1-click weather doesn't work. Waiting to see what other issues there are. Even though FF4 is faster, not a happy camper - QC seems to suck.
Tabbed groups is incomplete and not ready for prime time. No persistence between sessions.
And I have read that Mozilla may plan on faster release cycles - given FF4 had a lot of problems - especially with one of the main competitive features of FF being addons - seems like Mozilla is going in a very bad direction.
I might be able to help with that one.
Check the "When Firefox starts:" setting in Tools>Options>General. If it is set at "Show my windows and tabs from last time" then I lied, and I don't know what the hell is wrong.
If it isn't and is set to "Show my home page" then you can change that and when you re-start all your groups should be the way you left them.
Another option if you want to have FF start up in a homepage sometimes (I'm not sure why, you can just put the homepage in one of the groups ... but anyway ...) then you need to change a different setting.
For some reason the default on installation with FF4 does not display the "Save and Quit" popup menu when you shut it down anymore.
This is easily changed in the about:config preference settings. This link will show you how.
After "browser.showQuitWarning" is set to true the exit option window should start coming up when you quit FF. Just click "Save and Quit" and when you crank back up your tab groups should be there.
I have recently started using an add-on called Tab Mix Plus, which has a slightly better session manager than the one built in to FF4. You might want to look at it as well.
Sadly, none of this helps much if FF doesn't get to exit politely. I just recently learned that the hard way. I'm still looking for a more durable solution to the same problem.