I used and love TST (plus a huge number of extensions - TST is an extension that is extended with further extensions!) but it's complex and clunky.

Sidebery can do the 80% of TST that matters, with a better UI and UX and saner defaults. Also it has a feature to save and restore all tabs, with the whole tree structure preserved (even though I think it should be its own extension)

Only problem is that I suspect that Sidebery has severe memory leaks (not entirely sure it's the culprit though)