Error since upgrading to Firefox 1.01

I just performed the upgrade to Firefox 1.01 yesterday and have had a 
couple of serious problems since.

First, a lot of times when I try to execute the firefox 1.01 program it 
won't run. It appears as a process in my windows XP Home Task Manager, 
but it won't run. I try it again and all it does is add another process 
but still does nothing other than the mouse cusrsor momentarily (ie, 
about 4 seconds) switches to the loading cursor but then stops and 
nothing happens. The only way to get Firefox to start is to go into Task 
Manager and stop the firefox.exe processes and then try again and only 
then does it work. This happens still after numerous re-boots. I also 
probably made the mistake of upgrading from 1.0 to 1.01 via the browser 
functionality, but then after I started having this issue I uninstalled 
1.01 via the add/remove programs and reinstalled from the executable 
downloaded from mozilla and it still does it.

Second - whenever I do not have firefox already running, and I open up 
an email in Thunderbird with links in it and click on one of them, i get 
a pop-up error box telling me the following:

"The program must close to allow a previous installation attempt to 
complete. Please restart."

I've of course tried restarting and shutting down my PC, etc. I haven't 
uninstalled/reinstaled Thunderbird and don't think I should have to, right?

Thunderbird is my default browser.

Any help is greatly appreciated.

mark
www.sixstringtheory.com