WARNING: This addons is currently very buggy. Usually, it's a simple case of clicking a tab and a completely different tab is selected, every now and then. This is solved by going into Tree Style Tab's settings and unchecking and checking the "optimise tree restoration with cache" option. But today, I leave Tree Style Tab at the wayside, as my entire 70+ tab tree structure was completely demolished when I opened up Firefox for the day, only to see all tabs being considered direct children of 1 other tab, disregarding any previous tree structures. Disregarding the fact that I should probably get my tabs sorted out, it is clear that Tree Style Tab, currently at version 2.8.5, is too flawed for my uses. Tread with caution.