These extensions really help with privacy and security.
#0 Search Engine
Change your Search Engine, switch to #DuckDuckGo
Initially you will hate switching because the results won't show up as per your needs, but the search engine improves as you use it.
Okay I know this post is about Firefox but recently I've heard a lot about [Brave browser], and it also has an award system that gives you BAT(Basic Attention Token) which is a better way to support content creators. You can read about that here
Okay so this Extension by default Blocks all the Nasty Scripts that could potentially steal data, you can choose to disable or trust the website by clicking on the extension
The will essentially block browser trackers, plus provides an option to enable site privacy protection.
This is a bit off-topic, but helpful if you have a lot of tabs open.
Auto Tab Discard a lightweight extension that automatically reduces the memory load of open—but inactive—tabs. This also helps portable devices to save battery.
Its 2021 if your website is not using HTTPS you should install SSL or use something like Letsencrypt or Cloudflare. This plugin redirects all the websites to HTTPS, you can disable the redirection per website or completely.
#6 Popup blocker ultimate
The name says it all, useful to block annoying popups.
One Stop Adblocker
That's all. I use these extensions on a daily basis.
Hope this helps.