I loved this add-on for several years, after Mozilla removed the old Add-on engine and this emerged as a new alternative to the old add-on (whichs name I forgot). But development pretty much ceased (last update in 2020) + the performance is terrible, even on highend hardware. I then found out about "Simple Tab Groups", even with 1000+ Tabs this add-on doesn't struggle or slows FF down to a crawl like Panorama does.
Get Simple Tab Groups instead of this.