Yahoo! Search blog: Firefox Toolbar: Beta no more!. One of the nasty things about the yahoo search bar in firefox is that it silently and completely resets default search. Here is how to get back to the default where google is used:
# Type about:config in your location bar. This will display a list of configurations for your browser. The bolded ones have been changed from the default.
# Right click on the ones that have the Yahoo url in it and set it to “reset”. This will get you back to Firefox default settings
# 3. Close browser window and open new one. You should be all set.