Just want to remark that my answer above was medium- and long-term, and that others have stressed the importance of a good backup strategy. Here are some immediate suggestions, though I don't use Windows.
Geek's point is very well taken, though CodingJoy is using Windows. :-) From USCERT:
'Microsoft Releases Advance Notification for November Security Bulletin
added November 5, 2009 at 04:17 pm
'Microsoft has issued a Security Bulletin Advance Notification indicating that its November release cycle will contain six bulletins, three of which will have a severity rating of Critical. The notification states that these Critical bulletins are for Microsoft Windows. There will also be three important bulletins for Microsoft Windows and Microsoft Office. Release of these bulletins is scheduled for Tuesday, November 10.
'US-CERT will provide additional information as it becomes available.'
My immediate advice is always to change one's important passwords (bank, PayPal, Amazon) by way of a secure computer, then take yours to a consultant. They charge about $30 to use three or four of the best malware programs. You are likely to find more adware, spyware, & other malware than you think.
This problem sounds like a relatively innocuous variant of the old ZLOB trojan horse, usually propogated by clicking on a site's hyperlink to install a movie codec. (Always go to the site, such as Adobe, yourself.) However, always plan on the worst: the original stole passwords.
http://en.wikipedia.org/wiki/Zlob
If Firefox still points you to 'allthebrands', manually edit your DNS (domain name server) ip address during your session. (Sometimes a running program will change it back.)
CarlF's suggestion has been implemented. Judging by SpamCop's ever-changing list, one needs to identify the site, report the site (which Google has implemented), and a search engine can, well, do something. It's not as easy as SPAM. Legitimate sites can be compromised with web bugs. Finjan has a 'bot' run through the site before you do. Suspect sites that prohibit this.
Here's a popular site for malware specialists, with instructions.
www.geekstogo.com/forum/Virus-Spyware-Trojan-Removal-f37.html