Try clearing your browsing data, especially the cookies. (Restart after.) If the above didn't do, do the clean profile thingy - in the "FAQ" topic you'll find out how. If the above didn't help, try a thorough uninstallation. Then check your file system - like for errors and vestiges - and try a new, clean install. From a trusted site of course. Make sure it installs properly.

Then some.

By the way, what is your anti-malware software? They do happen to mess with various applications' stuff...