Exercise restraint, guys. Tab grouping is the classic engineer's solution to a non-problem.
People's browsing habits differ. Some of us do use multiple windows and tabs so we can switch our focus away from a task and return to it later. Mozilla's user studies and large-scale data mining through Test Pilot bear this out, e.g. http://surfmind.com/muzings/?p=505 - among other things, that analysis of several thousand Firefox users found that tab opening/closing behavior among the participants followed a bimodal distribution.
43.
It would be horrible to manage without any grouping mechanism and hierarchical organisation. Thanks Tab Kit.