[clumsysmurf]

I think it needs Vertical tabs at least

[gnicholas]

Tree style tabs kept me on Firefox for years beyond when I would have otherwise left. Now I use Brave with an extension that does an ok job of imitating TST. I really wish FF were performant enough that I could justify using it.

[throwaway67114]

Firefox has at least 2 tree style add-ons right now.

[pvitz]

Tree Style Tab does that quite well. Does it need to be built-in?

[eppsilon]

Sidebery is a pretty nice extension for that