I'm using ZA Extreme 9.1.008.000 with Forcefield 22.214.171.124 and had no problems running this setup on Firefox 3.5.4. But as soon as I upgraded to 3.5.5, Firefox won't launch.
I've tried un-installing and re-installing Firefox 3.5.5 and it still didn't work. I tried starting Firefox in Safe Mode and no luck. The only way I could get Firefox to run was to turn off Forcefield.
I didn't have this problem with Firefox 3.5.4, so there's something specific in Firefox 3.5.5 that Forcefield doesn't agree with...
(WinXP SP3 / ZoneAlarm Extreme Security 9.1.008.000 / Forcefield 126.96.36.199)