Hello.
Just today, A Mozilla developer has posted a article of why everyone should get rid of their AVs, except for MSE/Windows Defender. Here is the article: https://www.bleepingcomputer.com/news/security/former-mozilla-engineer-disable-your-antivirus-software-except-microsofts/
I don't know if I fully believe it, however, I never recommend ever paying for a AV because it is mostly a waste of money. Usually paid AVs don't do much more then a free AV would do for the average user.
I also seen that he recommend using Rust language as a replacement to C/C++ for Firefox, due to C/C++ having many memory vulnerabilities to it. Right around 2015, Mozilla actually was experimenting with Rust language for Firefox. I assume they probably have done a lot more sense then. Rust is capable of calling C++ programs in it, much like Go does, too. Using open-source languages is actually good because they are less buggy and much less security vulnerabilities in them.