What’s really annoying is that a lot of existing extensions already work. Mozilla just makes it unreasonably difficult to install them.
Change your user agent (using Firefox Nightly and the user agent switcher extension, which is supported) and you can install extensions exactly as on desktop.
That’s only telling half the story because often features silently failed for many extensions because of the great idea to switch from proper Firefox to the GeckoView based one which actually did not implement many APIs used by extensions.