this sounds like a problem with malware on your pc. please go to firefox > addons > extensions & disable/remove any entries from toolbars etc. that you have not installed intentionally. also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there and to a full scan of your system with the security software that you have in place.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

See also:

• http://www.imessengr.com/2006/12/how-to-remove-uninstall-sweetim.html
• http://www.sweetim.com/help_simff.asp

Go to search engine settings.Then click on the extension label.then u get number of extensions.enable which one do you want.it's working fine for google chrome.