Today 10 years ago I went to Poland to buy a Phone with pre installed #Firefox OS on. The Phone was a Alcatel One, so very shitty. Two years later I installed Firefox OS on my Nexus 5 instead.
It was a very good concept, but sadly rolled out on too shitty hardware so it never caught on.
Once Firefox lost session manager and downthemall, it was dead to me.
Nowadays I use edge. All the benefits of chrome plus it’s leaner.
I use kiwi browser on phones for the addons, and because it’s faster than Firefox
I haven’t looked into those specifically, but I’m pretty sure there are alternatives that do the exact same things for FF
I use Tab Session Manager and Session Sync add-ons with Firefox and I’m quite happy with them.