In the coming months Mozilla will launch support for an open ecosystem of extensions on Firefox for Android on addons.mozilla.org (AMO). We’ll announce a definite ...
I wonder if hidden tabs are. It's not that I want tab groups on mobile, but it'd be interesting to see attempts, specially with how absolute dogshit grouped tabs are on mobile chrome, specially if there's pop ups involved (an inversion from desktop chrome, which has the best grouped tabs)
That extension requires rather deep integration into the UI, which I don't think is possible for Android extensions. So, I doubt, it will become available...