Looks like you've got malware, which you will of course need to get rid of.

Go to the 3-bar menu (or   'Tools') => Addons => Extensions and look for any unfamiliar or suspicious looking extensions. When you find any : remove them.

Also look in : 3-bar menu (or 'Tools') => Options => Advanced => Network tab => Under : 'Offline Web Content and User Data'

However :   most malware will be 'hiding' somewhere , so let's run malware scans :

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.
They all work differently   -   what one program doesn't pick up, the other might.

Especially for Mac : https://www.malwarebytes.com/mac/

What great advice. I downloaded malwarebytes. Immediately it took care of being sent to places I did not want to go. It always seems to be Yahoo! Makes me never want to go to anything with a Yahoo name.

Forgot to mark response as CHOSEN SOLUTION.

Thanks for such a quick response.