thunderbird-user.js VS firefox-setup

There's this GitHub repo called thunderbird-user.js which is similar to (and also inspired from) the arkenfox project (for Firefox security and privacy tweaks). I suggest you check that out :)

I'd also consider taking a look at https://github.com/HorlogeSkynet/thunderbird-user.js I ported it from Firefox to Thunderbird, compared/looked at source. I handed over maintainer ship to someone else though and I don't personally use Thunderbird anymore. Nowadays I use a text client https://neomutt.org with a setup very similar to this.

If you don't wanna go through all this, you can also use user.js maintained by other people. Here's the link to my own setup. Other setup that I highly recommend is this one (I was using this before I created my own setup). The difference between the two is that I follow the suggested way of implementing your own changes in the arkenfox's user.js according to the wiki while the author of the latter one edits the user.js directly. I would still suggest making your own overrides for the arkenfox's user.js but if other's user.js satisfy your needs then that's fine as well.