Firefox is a web browsing client, not a server. BearShare is a peer-to-peer file sharing application. Are you talking about a default browser, or maybe a default search engine, or perhaps your server connections got changed?

http://kb.mozillazine.org/Default_browser

To change the default search engine used from the addressbar, change these settings in about:config:

• browser.search.defaultenginename - Google is default
• keyword.URL - http://www.google.com/search?num=100&q= is default

As far as connection settings go, I find that "No Proxy" works the best.

Type about:config in the Location (address) bar and press the "Enter" key. When you see a warning, click I'll be careful, I promise! button.

• Preferences that have been modified are shown as bold (user set).
• Preferences can be Reset to the default or changed via the right-click context menu.

-> In the Filter bar, type bear. This will show all bear related preferences.

• Reset all these Preferences to their Default values (right-click a preference and click Reset)

-> Close the about:config tab and then Restart Firefox.

Check and tell if its working.

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]
• [/questions/762144]