first, if the problem is occurring only in firefox and not in IE, it sounds like the problem is not being caused by a firewall in your router or in Zone Alarm ... i'm not a firefox user so i can't help much there ... it might be worth checking security settings in firefox ... perhaps you can reduce the security level a notch to see if that's the problem ...
to rule out other sources of problems, i would try to get down to the simplest configuration and then start adding things back in ...
for example, i would temporarily turn off Zone Alarm (remember to turn it back on) ... if you still have the problem, i would try connecting your computer directly to the DSL modem ... perhaps there's some type of built-in firewall in your router that causing the problem ...
and finally, if none of this helps, you might try giving your ISP a call ... sometimes they can trace what's happening between their servers and your modem ...
one more thing, spybot and adAware are great products ... you definitely should consider adding SpywareBlaster3.2 to your defense arsenal ... you can download a free copy
right here ...spywareBlaster runs on its own ... unlike spyBot, you don't have to remember to run it ... you should update the software periodically, however ... and, once you've installed it, make sure you go through every menu and activate all the protections ...
hope this helps ... good luck ... if you solve the problem, let us know how you did it ...