Tree Style Tab is THE reason I continue to use Firefox. It is a significant help in using the browser in an organized coherent fashion.
I have tried to use the roughly equivalent add-ons available for Chrome and Edge, and they are nowhere near as well designed.

Really enjoy this plugin but why isn't the tree structure persisting when I restart Firefox and restore previous session?

Very useful. Clear and friendly interface. Greatly enhances Firefox, tab overview, bookmarks use.

My experience with this extension is great so far.

Edit: I've found an issue. When I open all the saved pages/sites in a bookmark folder, the tree style tab sidebar suddenly started to flicker and it doesn't show anything - no window tabs.

Hey what happened to the close all tabs to bottom command? It was very useful for chain opening links or downloads and closing all at once...

This is just what I was looking for. I can find my tabs finally. This is great for keeping track of different tasks instead of having tons of windows to dig though.

Liking the new proton & photon style, but it would be great to be able to hide folded tabs from the top bar.

Other extensions let you hide folded tabs from the top bar. That way you only see their parent in the top tab view.