The thing that continues to infuriate me about tabs, is that we're expecting applications to provide them. This is a waste of time for application developers! The lack of tab support is a deficiency in the majority of window managers, that should be addressed (only) at the window manager level.
The proof is in how poorly tabs continue to integrate with OSes. Suddenly you need 5 or 6 commands to deal specifically with tabs, e.g. it seems there has to be a "Close Tab", "Open in New Tab", etc. in addition to "Close Window", all because there is no easy way for the application to distinguish one from the other. Minimization doesn't seem to do exactly what you want. And sheets on Mac OS X, originally awesome for their ability to not block access to more than one window, now end up blocking 20 tabs at once.
But even if this wasn't the case, who is to say that all my tabs should be web browsers? It is completely reasonable to want one of those tabs to be my mail client, a couple to be terminals, etc. with web browsers mixed in. The only sane way to achieve that is with window manager support.
Yes, some window managers have this, but only obscure ones. Until you have Windows and Mac doing this, Firefox won't stop doing it.