They didn’t disable it, they rebuilt the entire browser from scratch to re-base on their current desktop-grade rendering engine, and as a result had to port a lot of things and optimize in regards to android’s battery optimization.

They’ve finally finished doing that and can now begin the preperation for releasing this to the public.

No idea how good or bad this is but I saw a link to https://addons.mozilla.org/en-US/firefox/addon/tablet-ui-for-firefox/ posted somewhere a few days ago and still had a tab open.