Computer help: PHISHING ATTACKS

Well...

The added spam is a result of your careless action. You validated your address as being active, so now you're going to be flooded with spam. This is why most people have a secondary or tertiary email account just for things like this. If we have to sign up for some sight, and think we might get sent a bunch of stupid newsletters and other crap that's of no interest (like Cnet for example), you give the "spam" address. That way, it doesn't clog up your main email account, you can still get on to the page or service... And if the site sells your address to a spammer, or someone who then sells it to a spammer, it's all going to your "spam" account.

There's nothing you can do about the spam lists that already have your gmail account, but you can try and keep even more spam from coming by doing the above.

Your other problem is unlikely to have anything to do with your hasty actions. I haven't heard of a single bit of malware that affects Firefox. It may exist, I've just never heard of it. It's probably just a coincidence that you're more aware of due to opening yourself up to all that spam.