You could try to update the program - possibly some background upgrade didn't sit well with it and it has it like that. It usually works well for both Firefox and IE.
Alternatively, if you're using a PC, you could try to run the browser in safe mode, see what it does. If it still doesn't work, like Caeli said, you can try to uninstall & reinstall the browser - of course, helps if you can download the .exe file and save it like that before the actual uninstallation, unless you have a backup browser.