See:

• http://www.ehow.com/how_6609141_remove-bearshare-spyware.html
• http://www.fanhow.com/answers/question-77222-how-to-delete-bearshare-search-from-firefox

You can look for a "Mediabar" program under "Control Panel > Programs and features"

See also this forum thread about BearShare:

• /questions/792580

If like me, you have deleted all the bearshare you can find through searches and still have it popping up as your default search engine. There's a trick I tried and it worked. Open you're browser then do the following steps: 1. Click on tools 2. Click on options 3. Click on the privacy tab 4. There will be two options in blue. Click on remove individual cookies. 5. You can then clear all cookies, or simply remove all bearshare cookies in the list.

Hope this works for you like it did for me.