I've seen this happen a few times. Seems to be a firefox bug, not a virus of adware/spyware.
What I do is uninstall Firefox. Delete the profile folders (in [UserFolder]\Application Data\Mozilla and [UserFolder]\Local Settings\Application Data\Mozilla). Then re-download the latest version and reinstall it.
The Foxmarks Bookmark Synchronizer automatically synchronizes your bookmarks between two or more computers running Firefox. It also lets you access your bookmarks from any computer anytime via my.foxmarks.com. An easy-to-use wizard guides you through the quick startup process. Then Foxmarks works silently in the background to keep your bookmarks up-to-date on all your computers.
I have a question about Medicat if anyone can answer.. My windows install is corrupt and wont boot. Does Medicat allow you to run DISM online or do an inlace upgrade? Trying to do some sort of repair install or recovery without a fresh installation