I've wanted to install an extension from outside addons.mozilla.org, but Firefox didn't let me do it

So I've did a small research and looks like there are 3 ways to sideload extensions, but all of them suck

1. Using FF Developer Edition

In the Dev Edition you can set xpinstall.signatures.required to false in about:config, but the problem is that the Dev Edition isn't as stable as standard FF

2. Temporarily load the extension

In about:debugging#/runtime/this-firefox you can temporarily sideload extensions, but they will be removed next time you open FF, which is annoying

3. Modify FF code

Lastly, I found this script which modifies the FF code, but this can break things so I don't want to use it

I'm really annoyed that Mozilla gets to decide which extensions I can install. So... what's the best way to sideload extensions?

Edit: thanks everyone, I'm now using a FF fork (Librewolf) which lets me sideload extensions after disabling xpinstall.signatures.required