MUST HAVE & BEST addon even with 360 tabs grouped on the left side. Good performance even with 5GB RAM used for DNA & engineering on 64 bit FF ESR. I will stay on ESR 52 (32 and 64 bit FF) until this addon is properly and fully supported by FF and addon creator. If I have to I will stay with ESR 52 even when it is no longer supported in 2018. And I don't care if TST has some bugs; they're mostly minor and mostly affect the special case of 1 tab or 1 group of tabs. Work-around is to just have 2 tabs opened or more and it's perfect. I would pay $$$ to Piro for his great work !! Prior to using ESR I was fed-up with many addons and icons breaking with every FF update. I dreaded the updates but there's the security issues. I was spending way too much time repairing FF (non-ESR). Intel i7 and 16 GB RAM underused. They should have kept the older addons in a sandboxed/container within a 1 single thread. And add the newer web-extensions in their new multi-thread machine to avoid killing decades of software by hardworking dedicated addon developers. So much addon software destroyed in 1 swoop :( And I have over 50 addons. Even with the very hungry NoScript and other necessary privacy and security addons.