Just noticed that Mozilla now has an optional tabbed interface, ala NetCaptor, dubbed MultiZilla.
It works like crap here, but then, it's still alpha. I'm a big NetCaptor fan and am glad to see Mozilla heading in this direction.
Incidently, WebBlinds 1.1 is also supposed to provide an optional tabbed interface to IE. (That is, if they ever get done with 1.0.)