I was downloading a patch for World of War Craft, when my browser collapsed and I lost my bookmarks and the browser would not even take a bookmark when I rebooted. I downloaded FireFox again and did a fresh install. What happened was the bookmarks are still gone. The browser " vibrates and jumps"..shakes..burps? it moves and sometimes not. I scanned for a virus, did an add ware clean and spy bot scan. I never found a thing.
I didn't find the right solution from the internet.
your browser has likely been hijacked. uninstall the browser and reinstall it.