My address bar changes when I go to Google and press Ctrl+Enter.
Both Firefox and Internet Explorer behave like this.
It sounds like you've got some malware. I suggest you go grab Malwarebytes Anti-malware (the free one) and Spybot S&D. Run these in safe-mode, and run your anti-virus (Avira and AVG are both good and free). You should probably take this opportunity to backup your important files, these things can get to be a serious pain and it'd be nice to not lose your tax info and precious pictures while trying to remove the stuff.
Also, make sure you're all up to date with your windows updates (and get microsoft update to make sure your office apps are up to date). Additionally make sure IE is at version 8 (or at least version 7). And run add-remove programs and remove suspicious evilness.
You may also need to use HijackThis to remove evil BHO and auto-runs. Or run regedit
and check for suspicious things at the following locations:
There are more, but those are the common ones where evil likes to hide.