You need to delete your cookies then use the tools I suggested. Your not infected by anything bad. You have tracking cookies on your system. Every site use's tracking cookies. With out them you wouldn't be able to log into your favorite sites or even look at video. You need cookies for almost everything anymore. You want to do is get rid of the ones that aggravate you and keep the ones that don't.
CCleaner does a good job of deleting cookies.
Download it and run it. Keep the default settings with the exception of tracking cookies, enable this for deletion. Run a system restore first, and stay away from the registry cleaner unless you know what your doing or are prepared for the possible consequences.
Once you delete the cookies, any user I'D's and passwords you have saved will be deleted (they are cookies to). Then set up firefox to keep the ones you want. This with the tools should take care of it. I hope
LOL!
Chris