Yahoo is not included as an option in Firefox, so why is it showing up? That's what we need to sort out to solve this problem.

Step #1: Investigating Add-ons''

You didn't share your extensions list while posting your question, so here's how to check for problem extensions on your Firefox:

Open the Add-ons page. Either:

• Command+Shift+a (Windows: Ctrl+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything that mentions Yahoo, or search, or privacy, or looks suspicious, or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Any improvement?

If your Add-ons page is blank or is blocked, you can restart Firefox in its Safe Mode to do the above review:

In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to bypass issues that can cause problems with pages.

If Firefox is running:

You can restart Firefox in Safe/Troubleshoot Mode using either:

• "3-bar" menu button > Help > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)
• (menu bar) Help menu > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)

and OK the restart. A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

If Firefox is not running:

Hold down the option/alt key when starting Firefox. (On Windows, hold down the Shift key instead of the option/alt key.) A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

Note: Don't use the Refresh without first reviewing this article to understand what will be deleted: Refresh Firefox - reset add-ons and settings.

Can you regain control of your searches?

As of Firefox 57.0 and later any locales of Firefox that had Yahoo as the search engine default was changed back to Google as the default ...reluctantly and Yahoo was completely removed from Fx 59.0 and on. https://blog.mozilla.org/blog/2017/11/14/firefox-features-google-as-default-search-provider-in-the-u-s-canada-hong-kong-and-taiwan/

Some of the known reasons for the change is in https://blog.mozilla.org/blog/2017/12/05/mozilla-files-cross-complaint-against-yahoo-holdings-and-oath/ and https://support.mozilla.org/en-US/forums/contributors/712925

So how are you seeing Yahoo in Firefox?

To see Yahoo something in Firefox could be due to some maleware or a Extension that added it.