Seeing all your chat twice? This cropped up after a recent Norton antivirus update. The fix has been to uninstall and reinstall Norton according to these instructions:
We've just provided the Phoenix-Firestorm Preview Group with a release candidate for our next release. If you would like to be part of our testing process by using this build and providing feedback before
If you're ever looking for a setting and don't know where to find it, try the "Search Settings" and "Search Menus" bars, located in the Preferences window and the upper menu bar, respectively.