I use Sidebery, which is similar, but adds features like 'panels' (essentially switch between sets of tree-style tabs in the sidebar) that integrates with Firefox 'containers', so you can have a 'work' vs. 'personal' panel&container for example.

The tabs being listed vertically is by far the most important aspect to me though, I previously used something (that stopped being maintained) that did that without being 'tree-style'. Nesting is probably not what I wanted as often as it is.