The release notes honestly weren't all that helpful - but looking over the Git repo, it looks like a lot of the major crashing/session restoration bugs were squashed in 2020-2021 and the backup functionality was improved enough to make backups more user friendly and somewhat more automated (aka: worth using and not 4 days out of date). There are still some flaws but those flaws come from the extension suffering the limitations of being a web extension - which is a tangentially related but another huge gripe of mine.
Now if only I could find a way to restore my context-menu tab switching - a feature lost when FireGestures was killed off. I didn't use any of the other gesture functionality at all - I only used the "[Popup] List All Tabs" feature which worked great with tab groups back in the day. (See: "Wheel Gestures" http://www.xuldev.org/firegestures/features.php)
E: (moments before I was about to post...)
Holy. Shit. Gesturefy recreated that functionality - and around the time I had given up on FF too. Back to Firefox I go! I had tried Foxy Gestures thinking it was the successor to FireGestures but I never gave Gesturefy a chance back then. In case I was bad at describing it, you can test it out yourself after setting it up in the settings: "[Popup] All Tabs" as a wheel gesture - it is an absolute game changer and I am SO GLAD I can go back to my circa-2013~2016 workflow after all these years. Only downside is continuing to scroll doesn't highlight tabs to change - so a small step back - wonder if it is even possible with how WE's are limited.