You'd rule out malware? It's the first thing I'd check for. I've had redirect viruses that behaved exactly like this.
Tried disabling ZoneAlarm? That'd be #1 with a bullet for me, a program which controls other programs internet access on a case by case basis = sounds like your problem.
What OS? Newer ones with Microsoft's firewall, if it's not disabled and running concurrently with ZA can cause problems.
If, somehow someway, two browsers got screwed up running a proxy or something.. Unlikely. But it could cause what you're describing. Also if you've updated your router's firmware or hardware or tweaked with the settings lately, it could cause a targeted connectivity issue like this.
About the only thing I would rule out is mal-ware/hackerz. Highly, highly unlikely. Regardless, fish boy should stick to selling fish. 'You're infected, but tough luck. Enjoy having hackerz racking up your charge cards, loser!' If it is, which I feel safe saying it isn't, I can only shake my head at advice saying there's 'nothing you can do.' There's plenty you can do, and nothing that can't be removed.
Try installing another browser, see what happens? Chrome, Opera, whatever. Might focus us more on if it's a browser/www issue only, or just a Firefox and IE only. I'll try to remember to pop back in here later tonight should you have further data/questions.
Right now, on very limited information, I'd bet the farm it's coming from Zone Alarm. So focus there first, imo.
