Have just started using this with FF57, as the "list tabs" drop down that I'm familiar with from v. 56 and earlier seems to have gone AWOL. Tree Style Tab addon meets this need nicely, even if a bit more cumbersome than the old button used to be.

On the plus side, it has more features that I'm guessing I will grow into: it took me a moment to find the "expand/collapse all" toggle, for example, but it's there! The themes are decent, but I would prefer one that didn't differentiate the "sidebar background" from the "tab background" -- perhaps there is one already, though. Also, it would be nice to have an option with more compressed presentation.

On the whole, though, quite a valuable addon, and kudos to the developer for having this ready to run in the new world of Firefox Quantum.