I also used to be a Thunderbird lover, but I was forced to ditch it due to crippling freezes, crashes, and slowdown when you have a lot of emails. Mozilla just feels like an awful steward of their projects at times.
EDIT: I also subscribed to Mozilla VPN for almost two years and was forced to ditch that too, due to... solvable technical issues, again. Mullvad was just a greatly superior product for the same price. I still use Firefox for all my browsing on desktop and Android at least.