Problems after install of Firefox 3.0

I installed Firefox 3.0 on a clients laptop running XP SP2.  After using it a while suddenly there was a pull down screen taking up about half of the browser window.  Its a totally gray window below where the web page is displayed and above the bar that says done, taking up the entire width of the screen.  

I can go to boundary of this gray windows where it meets the web page window and see double arrows.  I can then pull this new window down to make it just about disappear.  The best I can describe it would be the type of window resizing one can do with most email clients.  But I cant make it disappear completely and then whenever I close and reopen Firefox the darn thing is there again.  

I have cleared out the cache and private area.  I have uninstalled 3.0 and reinstalled version 2 and now its there in version 2. Then I cleared out everything again and reinstalled 3.0 and its still there.  I cant give my client their laptop back until I fix this.  

I also would like to know peoples opinions of Firefox 3.  Should I be upgrading my clients computers to this or such I stay with 2 until all the bugs are out?  One reason I started upgrading was because of a problem where Firefox 2 used large amounts of memory and doesnt seem to return most of it when the application is closed.  I was hoping this might be fixed in 3.

Thanks,
Al