Uninstall search plugins
From MozillaZine Knowledge Base
This article does not apply to Firefox 2 or later. Starting in Firefox 2, you can remove search engines using the new search engine manager, accessible by clicking on the Search Bar icon, then clicking on "Manage Search Engines" from the drop-down list.
This article describes how to remove search engines from the Mozilla Suite / SeaMonkey Internet Search preferences or from the Search Bar in Firefox 1.5.x and earlier.
With the application closed, open the searchplugins folder in the following locations. Note that Firefox 1.5 and SeaMonkey place manually installed search engines ("custom" search plugins) in the profile folder so you may have search plugins in two locations.
Delete both .src and .gif or .png search plugin files for the search engine you want to remove. For example, to remove the Webster search engine, you would delete the files "webster.src" and "webster.gif". Restart the application and it will be gone.
If you removed a search plugin because it was broken, please go to the Mycroft Homepage and "judge" this plugin.
Search plugin managers