This may have been adequately covered already but, just to add my two cents...
I recently (this A.M. in fact) upgraded to ZA SS 2010 (NOT 'Extreme') after which I started encountering problems with FireFox 3.5.5.
a) I could launch FF ONCE after a reboot but
b) I could NOT EITHER launch a Second Instance of it 'EXPLICITLY' from my desktop OR 'Open a New Link' in a separate windows (eg. from a Google search) though
c) I COULD Open such a link in a 'new Tab'.
Checking 'here' (at these forums) I noticed that several people seemed to be experiencing similar problems BUT ONLY with ZA 2010 'EXTREME' which I NOT used as the source for my upgrade.
Further research with Process Explorer (Get It If You Don't Have It!) led me to notice
d) That If I 'Killed' FF (which was still 'running' even though there were no FF 'Windows' running OR on my taskbar, I COULD 'restart' the whole chain of events/problems at '(a)' above...
While in/using PE, I happened to notice that a ZA FORCEFIELD instance was also running... To me this was a surprise as I thought I would never 'see' that as I had not used ZA 2010 EXTREME in my upgrade...
Ran a few more tests but, not to bore you with the deatils, wound up (as far as I can tell) resolving the whole FF 3.5.5 problem by
e) Shutting down ZA 2010.
f) Using Add/Remove Programs to Uninstall ZA FF (which I did not expect to 'see', as 'above'), and
g) Restarting ZA.
So far/NOW, everything seems to be back to normal.
Except for HUNDREDS of False Alarms I seem to be getting... In THIS CASE, with respect some Symantec Norton System Works folders...
I always install and use some Norton System Works 2003 components on my systems - specifically Norton System Doctor 'cause I like the disk, CPU and other monitoring info available in it's 'flyout' AND to be able to use it's Norton Protection/Undelete capabilities which can trap 'Console' deletes.
NEVER had a problem before with this (ANY prior release of ZA) and never expected one as NO SYMANTEC anti-virus, anti-spam, et al components are installed and 'besides', the problem I encounter has to do with some folders/files that NSW 'Protection' maintains on each drive:
Every Single (hidden) File (ASAIK) in a hidden folder on each drive (eg. C:\RECYCLER) shows up as a virus/threat, as well as NPROTECT.LOG (file)).
(And they DEFINITELY are not (all) threats...).
Anyway, I solved THIS problem by simply configuring ZA IS 2010 to IGNORE/Not Scan C:\Recycler...
(I never set up regular scans on my other drives as they would take too long and just run them from time to time as I wish...)
Anyway, hope this (above) is of some use to others who may be having similar problems...