So I used to think TST was great, but this... this takes it to another level. The out-of-the-box experience is great. There's a lot of features, the UI is coherent in it's design, which is pretty damn neat, and to top it all off it kept my hierarchy from TST. I couldn't have asked for more.

P.S.
To have the colors of the browser match colors of the sidebar I got the "Dark Theme for Firefox by Stefan vd" theme. I could have done it the other way around but I like the warm gray better than the proton gray honestly. And it matches the userCSS I use for making all the "about:" pages dark :)