> It turns out there’s only 84 thousand Firefox extensions.
On addons.mozilla.org, but you can distribute Firefox extensions without posting on addons.mozilla.org. I do.
Other examples I recall when looking into this: Zotero browser connector for Firefox, Chrome Remote Desktop for Firefox (I think it adds a few features for connections to remote desktops)
I'm pretty sure that there were much more XUL and XPCOM extensions back then +10 years ago before mozilla pulled out the plug for that platform and moved to WebExtensions