My search engine by choice is Google but last week I decided to use Bing. I changed the search to Bing, did my search and then attempted to change the search engine back to Google. FF 4.0 Beta would not keep Google as the default search engine. It would always revert back to Bing after every change and search on Google.
I had to stop using FF and switch to another browser until I rebooted the machine and everything has been fine since.
Are you talking about the Firefox Search bar, that is to the right of where you type web addresses? By default, the Search bar is part of the Navigation toolbar - but it can be moved to another toolbar by the user.
Or is that a search function part of the MSN@Toolbar that shows in plugins as being installed?
I have changed the "about:config" settings mentioned here and the "Keyword.url" setting as well several times. No matter what I do, it keeps defaulting back to Bing. Unfortunately, Bing is blocked from my workplace firewall for whatever reason and I keep getting "STOP" screens when I search.
At the top right hand corner of your Fire Fox browser there is the search BOX you type in when you do a search. Just on the left side of that BOX there is a drop down menu. Choose which one you want to use by clicking on it. That will work!
I had the same problem with Bing and couldn't find it anywhere and no matter what I did I couldn't get rid of it.
But I found this solution and I hope it works for you.