The free version of this (I've never paid for it) is very good. I mostly use it for ad blocking with only the occasional scan for viruses. Ad-blocking-wise, it is very, very good. It even blocks the ads on youtube, though it takes about two seconds for the page to reload after it blocks the ad.
It hasn't yet caught any viruses on my laptop, but that might be because there are none?
The virus scanner only takes like five minutes and it can run in the background while you do other things.
All in all, I really like malwarebytes, it meets all my requirements, though I do use it mostly to protect my browser, and use a separate app as a VPN and download-checker (like it checks the things I download for viruses).

good

I work at an I.T. place and it is a weekly occurrence for individuals to bring in their computers claiming they have malware because they got redirected to an adware or malicious webpage.

I've never once encountered such an issue myself. Part of it is just making smart choices online (I.e. Perhaps don't click that random ad... Or go to that sketchy website..) and part of it is using this extension.

10/10 I recommend. Plus it's free!

Works fine for Firefox, does it also work for Google Chrome and the rest of my computer?