I need Firefox help

Last night I made the mistake of downloading software after a few scoops.
I downloaded a codec pack but mistakenly downloaded a Bing search toolbar. It also changed my home page to Bing and my search engine to Bing.

I've removed the toolbar and put my homepage back as it was but I can't seem to change the search engine back to Google.

Click to embingen

Does anyone know how to change the default search engine back to Google without re-installing Firefox?
I'm running Firefox 7
Thanks