> On the normal version of firefox for those platforms you can't permanently sideload an extension ...

Are you sure about that?

I am using Firefox on Windows and I currently have no problem sideloading extensions. They stay enabled and even update automatically.

Try, for example, installing this [1] bypass paywall extension via the "Download and install the latest version" link. Works flawless. ... or am I getting something wrong?

[1] https://github.com/iamadamdev/bypass-paywalls-chrome/blob/ma...