I just wanted to use this plugin to organize parts of my >200 opened tabs. After creating a group, I wanted to open one tab from the group. All tabs in the group were opened in a new window, thus I closed the window because I just want one tab from the group. After I closed the window, no firefox instance was running anymore, the session restore didn't work and all my tabs were gone. It would be very nice, if this plugin shows a warning on exit, if there are ungrouped tabs opened.