The default search engine in Firefox is Google. However, it is very easy for add-ons to change it to the search engine of their choice.

Try disabling all non-essential add-ons here:

orange Firefox button or classic Tools menu > Add-ons > Extensions

In particular, look for "Bing" items, "Search Helper Extension", "Startnow", "Vuze" and anything else that sounds nonessential. If in doubt, click the More link and see whether it mentions using Bing technology.

Once you're down to essentials, restart Firefox, change the about:config setting yet again, and see whether it sticks.

If you do not keep changes after a restart then see:

• http://kb.mozillazine.org/Preferences_not_saved
• https://support.mozilla.org/kb/Preferences+are+not+saved

Start Firefox in Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

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

• https://addons.mozilla.org/firefox/addon/searchreset/

Thanks guys --for the help - I had Vuze as a Firefox add-on... once I disable it and then changed the URL- config - Bing seems to be gone

Thanks for the help -- I love Firefox -- used it initially to get away from IE and Bing

Keep up the good work