Even do I would like there were more addons to choose from as default I can understand Mozillas choice here. And that is that most addons are not design for android and they would not work or give a very bad UX. So for many non tech savvy standard users, that just would be frustrated and blame Firefox, this decision can make sense to select god and popular addons they know works well.
But it would be great if more addons could be added ofcourse, and that Mozilla could have some design guidelines for new addons that they should work for both desktop and mobile (where it make sense). And mark in the addon store which addons that are design for both. Or maybe have a simple setting in Firefox for android that is for advanced users, there they could add any addon, but first they have to check a box that they understand that the addon may not work correctly on a smartphone.