Before they had to be made specifically for Firefox for Android. Once they finish implementing WebExtensions it'll be able to install any WebExtension. I'd say that's a lot better than before.
I'll add that the few extensions already available were well-picked and honestly already fulfill all my needs.
About 8 currently. But they're still working on enabling more. And they haven't pushed the new version to the stable channels yet.
How many plugins work with the new Firefox on Android?
> standard extension model
One were Google already declared that APIs used for ad blockers are considered deprecated and might be dropped at any time? With one major browser vendor being actively hostile towards a large amount of plugins that "standard" doesn't do much. It certainly doesn't guarantee portability unless Mozilla completely jumps the shark and also kills ad blockers.