Virus Removal Help please!

OK so I downloaded a few plugins for firefox. They were NoScript, VideoDownloader, and Faster Fox.
Right after installing them, every so often when I tried to load a different website FireFox would just take forever trying to load it, but it never could load the page. I have to open up taskmanager and shut firefox down everytime it does it.
I went to the norton's site and did a virus scan and it said that I had Adware.MWSearch on my machine. Well I downloaded the latest updates for Nortons and ran the virus scan and it found........ nothing. I ran Adaware also and that came up with nothing as well... but everytime i run a scan on the norton's website it tells me I still have this thing on my machine. I've downloaded a few other antivirus programs to try and remove the stupid thing but they also come up with nothing.

I'm really hesitant to mess with the registry keys like norton's suggests because there are a million files to go through and remove[/img] for this one and I really don't want to mess up my computer anymore than it is messed up, and it's not something i'm familiar with doing. I wouldn't know if I was deleting an important key or not basically.
How can I get this stupid thing off of my computer? Please help!