Sidebary v5 from (https://githu.boo/mbnuqw/sidebery/releases) is better.

This is an amazing sidebar hierarchical tab extension for Firefox. Saves a lot of time and allows you to keep regularly visited sites and related sites and pages together. Multiple panels of tabs, pinned tabs, the features go on and on. Few other options are even close. Nothing on Chrome is anywhere near as functional.

Fantastic tab management

Switched to Sidebery from Tree Tabs, definitely better, especially regarding performance. I have 300+ tabs, since I switched to Sidebery, Firefox's RAM usage is half.
https://support.mozilla.org/en-US/questions/1396277
Sidebery solved that successfully.

The only option I miss is unloading tabs/pages upon a predefined time interval. I'd set it to 1 week.

Tab Management 5.0. Best Tab Organizer. Must have! I have tried various and this is best in stability and functionality.

I was a user of TST, but it's full of unfixed bugs and a ressource hog. SireBery solves ALL the issues I had with TST ! Amazing !

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the best addon I have ever had. I can't imagine a web browser without this