Why does Firefox mobile still have so few add-ons?

You need to create a collection and then you can use almost any extension (it's a pain in the ass to setup)

https://support.mozilla.org/en-US/kb/how-use-collections-addonsmozillaorg

Mozilla is so stupid sometimes... It makes it feel like they are trying to discontinue all extensions.

Idk, but I'm still annoyed that pressing the search bar at the top hides the tabs button

If you use Nightly or Beta you can use pretty much any addon with a few steps: https://www.ghacks.net/2022/10/20/firefox-beta-for-android-now-supports-custom-add-on-collections/