Hi dan129, is this problem on your Mac? A moderator can move your question in that case (this forum is for iOS devices like iPhone and iPad).

On Mac:

As you know, Firefox doesn't include a Yahoo search plugin, so this probably was added by an extension or external malware. Here are my suggestions for investigating:

Extensions

You can view, disable, and often remove unwanted or unknown extensions on 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.

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 search or privacy? Anything 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?

Malware

This is a well-regarded scanning/cleaning tool for MacOS: https://www.malwarebytes.com/mac/ (no payment required)

By the way, does your Preferences page, Search panel, show a "Restore Default Search Engines" button near the bottom? If so, does that re-populate the One-Click Search Engines box and allow selecting Google or another search engine as your default?

neither of these suggestions were actionable. no yahoo add-on in extensions. and no button at the bottom to restore default search setting.

You have no extensions at all on your Firefox, or only extensions you totally trust not to modify your search engine preference?

Could you open the following internal page and see whether it lists any active policies (type or paste it into the address bar and press Return to load it):

about:policies

only extensions are honey and webex. nothing about search engines.

checked the policies. nothing active. this is what it says: "The Enterprise Policies service is inactive."

Perhaps one of the settings files has become corrupted. You can remove the file and have Firefox rebuild it. Here's how:

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, on the Profile Folder row, click the "Show in Finder" button. If Finder highlights an icon with a semi-random name like a1b2c3d4.default, double-click it to display the contents of that profile folder.

Leaving that window open, switch back to Firefox and Quit, either:

• "3-bar" menu button > Quit
• (menu bar) Firefox > Quit

Pause while Firefox finishes its cleanup, then rename search.json.mozlz4 to something like searchOLD.json.mozlz4.

Start Firefox back up again and it should rebuild the search engine lists for the Preferences page. If you return to those settings, can you access Google and the other built-in choices? See: Change your default search settings in Firefox.