hi, firefox lets you freely choose your search engine: Use the search bar in Firefox if this selection doesn't "stick" then something is wrong on your system (maybe adware or some sort of corruption of the configuration). for a start, please go to the firefox menu ≡ > help ? > troubleshooting information, copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on...

On Mac, this most commonly seems to be caused by Spigot or Conduit add-ons, or something else that snuck in undetected with some other software you downloaded.

Please try disabling ALL nonessential or unrecognized extensions on the Add-ons page. Either:

• Cmd+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then, if in doubt, disable (or remove). Especially if you find something called SearchMe.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Does that help you regain control?

https://blog.mozilla.org/press/2014/11/yahoo-and-mozilla-form-strategic-partnership/

Mozilla wanted to get more away from what Google is as Yahoo has been the default search engine in en-US Firefox since Fx 34.0 while other locales changed to other defaults.

You still have the Google search engine you can change back to.