On installing this addon, it immediately closed my Firefox window, along with all my tabs, and opened a new window without any of my tabs. Luckily I knew I could bring back my old window with Ctrl-Shift-N, but this is very non-user-friendly. When I install an addon to organise my tabs, I don't expect the first thing it does to be to close them all without asking me, or telling me how to get them back.