use the searchreset tool and delete the user.js file in your profile folder, refer to links below.

• https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save#w_user-js-file-overriding-preferences
• https://addons.mozilla.org/en-us/firefox/addon/searchreset/

i have find a definite solution of it , i was also suffering from the same problem i found a solution on website see below

http://www.ohotech.com/2011/06/how-to-get-rid-of-conduit-search-engine.html

Note that current Firefox versions no longer use the keyword.URL pref unless you would have an extension that restores this support.

The way such toolbars install can change an any moment, so what worked in the past may no longer work now and in the future other steps may be needed to remove such a toolbar completely.

Usually two things are necessary:

• uninstall (or disable) the extension(s) that add the toolbar.
• reset all prefs that have been modified or added by the extension and also check for the presence of a user.js file in the Firefox profile folder

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• http://kb.mozillazine.org/Preferences_not_saved

I came across this video. How to Remove Conduit Toolbar from Mozilla Firefox Completely

Hope this helps.

edit by a moderator

• see also Remove a toolbar that has taken over your Firefox search or home page
  • https://addons.mozilla.org/firefox/addon/searchreset/

The SearchReset addon installs, fixes some of these things and uninstalls itself. That is a quicker and easier method for some of the steps compared to the the method given in the video,

If you prefer to remove it manually, follow these removal instructions:

http://toolbar.conduit.com/changing-search-settings.aspx

http://deletemalware.blogspot.com/2012/01/searchconduitcom-uninstall-guide.html

However, you may also use AdwCleaner and Malwarebytes to remove Conduit and restore default settings and preferences.

http://www.bleepingcomputer.com/download/adwcleaner/

http://www.malwarebytes.org

Cheers!