Why won't Firefox open any tabs?

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Hi. Got a problem - been using Mozilla Firefox for yonks but after I shut down the system it conveniently installed updates. Now, it won't open any windows! The browser itself seems to work okay, the addresses come up in the address bar etc but all I get are empty tabs coming up - hitting return doesn't help. It seems google etc have stopped communicating with my browser. I'm running on Vista with Panda antiviral software, which isn't updated yet, so I think that might be the problem. I can use Google Chrome okay but I prefer Firefox - it's more versatile e.g. saves logins. Any ideas how to restore Firefox? Cheers!