Rated 4 out of 5 stars

No longer works in newest versions of FF. FF has become too restrictive in what's allowed, much like Chrome has been for several years now. Too bad, they were the best for customization, but now there are fewer and fewer reasons to not just use Chrome instead, it's more stable and it's MUCH faster. Side note: Anyone reading this should give Pale Moon a try. It was originally based on the older versions of FF that everyone loved, but it has forked off into something of it's own and it is a great browser for people who like to make a web browser "their own" via custom buttons, visual tweaks and customizations, extensions, etc.
And the best thing is that all of Button Guy's extensions still work with the newest version of PM. Hallelujah!
I'm giving a 4 star review based on this fact. :D

If it ever becomes possible to update this extension to work as a WebExtension, I would. I don't see it happening though.
Trying slowly to update extensions to work with the new system, but it is slow and needs a lot of rewriting of code.
And yes PaleMoon is a good option for some of the extensions. If you want versions that work best with PaleMoon, those on my website are the better option. Those here will not all work now, as some have moved to being WebExtensions.