This is the first extension I download with a new Firefox installation. In the settings menu, select "learn to block new trackers", then "show domains that don't appear to be tracking you", and go to websites that are known to have heavy advertisements, then start manually "training" the extension.

I also use this extension, with additional dedicated ad blocker, when setting up devices for older folks and friends who aren't super tech savvy. You can "set it and forget it" easily, and when configured properly it doesn't interfere with regular browsing. It blocks a lot of malicious advertising / phishing attempts before they happen. I find good ad-blocking protection to be more effective than running AV software as a first line defense. You can't click a malicious link if you don't see it. It doesn't replace anti-virus / anti-malware, but augments it very well.

Privacy Badger by EFF is by far the best Firefox extension, and it comes from a trusted organization that's legitimately dedicated to privacy. I would give the extension 10 stars if I could.