ads showing up on my Mac

Try Malwarebytes for Mac, sounds like some form of malware.

Q-6

 

MalwareBytes for Mac: https://www.malwarebytes.com/antimalware/mac/

 

A lot of ads have started showing up on websites that start from one side of the screen scroll and scroll across as you scroll down or up. Yahoo is full of them.

They are handling the javascript scroll event. There is little you can do with them except to disable javascript, but that would break other features you might want on page.

 

Wipr or AdGuard will fix that, from the extensions gallery

Q-6

 

Have good luck with uBlock. Prefer it over adblockplus.