Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; (<Control> [Mac=<Command>] <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Remove “ Yahoo “ Anything.

Also remove SafeSearch, SearchAssist Incognito, FileConverter Addon, SearchLock, DiscreteSearch, WebSearch, Findwide Search Engine

Now do the same in the computer’s Programs Folder.

Windows: Start > Control Panel > Uninstall Programs. Mac: Open the Applications folder. Linux: Check your user manual.

Thanks for your quick response. When I followed the directions above, my mac just reverted to my google home page....info is useless. Need help with mac desktop in removing any and all yahoo information. Thanks, Pat

Did you check out 'Also Remove' above?

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Now in the Reply Box on the forum page, do a right-click in the box and select Paste.

This will show us your system details. No Personal Information Is Collected.

Hi Pat, is your default search engine setting getting changed?

If so, what is the exact name of the unwanted search engine. This article will get you to that part of the Preferences page:

Change your default search settings in Firefox

If you change it to Google, does that work? How long does it stick?

It has never stuck before and after a thorough search of my computer i can not find any reference to yahoo. I will give it one more try. Thanks....

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.