I use Safari instead of Firefox because the swipe gesture to go forward and back works so much better. I love that I can swipe away half the page, get a peek at what I'm going back (or forward) to and then return to the page I was on without triggering a reload or anything happending. It breaks some sites a little bit (GitHub especially) but it looks cool on most of the Internet so I'm fine with it.
In that case, both MDI and tabbed UIs remove the capability of the WM to manage that specific rectangle of content, and require you to use in-app controls, which may not even exist.
This is especially pronounced for those who use non-standard window managers, say Ion or Awesome window manager which let you tile new windows rather than having them appear whereever they choose.
Dunno if that's jwz's reason, but it's one good reason that I've had in the past (although not for browsers, the number of tabs I keep grows too rapidly to manage nicely alongside long-lived windows)
The Apple 'our way is best' approach is often great, but when it fails, you're stuck without easy (or even hard) ways of fixing it.
You can also switch between windows with the Command-backspace key and with Expose (if you are on Leopard or Snow Leopard) or Mission Control (if you are on Lion), but those are pretty lame IMHO.
>The difference is that, on the Mac, for jwz, it works well with Safari and not with Firefox.
Not true: on the Mac, switching between the windows of Firefox works the same way as switching between the windows of Safari.