Try reset your search engine with this addons:

• Reset Search

Also:

• http://kb.mozillazine.org/Preferences_not_saved
• Preferences won’t save

Reset search didn't work for me, I don't know how to use it.

The SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).

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

• Do NOT click the Reset button on the Safe Mode start window.

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

If you do not keep changes after a restart or otherwise have problems with preferences, see:

• http://kb.mozillazine.org/Preferences_not_saved

You can delete a possible user.js file and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Director: Show Folder (Linux: Open Director; Mac: Show in Finder)

I tried the Safe Mode thing before, and that didn't work.

I notice that the screenshots show Firefox in Private Browsing mode (purple PB mode Firefox menu button).

Does it make any difference if you run Firefox in normal mode?

Did you check for issues with the preferences?

• http://kb.mozillazine.org/Preferences_not_saved

Used Firefox in normal mode: same result. How it should be by default: http://i.imgur.com/qlnsfEj.png How it is by default: http://i.imgur.com/0fhqmxz.png

Open Help > Troubleshooting Information.

Near the bottom, above Graphics see if you have a user.js line.

user.js Preferences

Your profile folder contains a user.js file, which includes preferences that were not created by Firefox. 

If you do see that, open that user.js file (it is a hyperlink) and see what's in that file. Whatever messed up your URL search preference probably added that user.js file; if that's the case, until you delete that pref line or the entire user.js file whatever you do to try to fix it that file will reset that pref after Firefox is restarted.

Didn't find a user.js line.

Hi,

What you describe is usually the result of a unwanted toolbar. Have a look at the 2 URL's below and see if that helps you identify the culprit. Good luck.

http://kb.mozillazine.org/Uninstalling_toolbars

https://support.mozilla.org/en-US/kb/remove-toolbar-has-taken-over-your-firefox-search

Type about:config in as URL Then search for "yahoo" in the long list that you see. I found 3 references. Right click each one and "reset". That stopped my problem of yahoo search showing up in each new tab. I too got dumped on by a so called safe installer and ended up with unwanted programs.

All of them have the "Reset" grayed out.

Only the default ones do. The 3 about yahoo were "user set" and the reset wasn't grayed out.

Actually, I don't search to Yahoo anymore. I don't know what fixed it, but it's fixed. The only thing now is that sometimes when I google something, it takes 5 minutes because a script or something stops working