You can find out right now. I've been using it along with old.reddit redirect for years on mobile.

The truth is Firefox mobile has been able to run desktop add-ons this whole time. All that happened was they had to restrict availability of add-ons from the addon store to only the handful that they had verified work without issues. All the other add-ons could still work if they were maintained, but Mozilla couldn't guarantee they'd work yet, so they wouldn't let you install them directly like the other add-ons.

But if you used Firefox Nightly, there was a built in work around that would let you use any desktop addon on mobile. Some don't work, some do. Old.reddit redirect and RES both work.