You can use Ctrl-Tab in Firefox (so not much difference). If you use ALT-Tab a lot, it is only a slightly different combination (depend how fast you ALT-Tab as well)
I think Mozilla is less about getting people to use their software, but more for other browser to keep up with standards. CSS 2 came out in 1998 - 2 years before IE6, PNG came out in 1996. Considering PNG is superior to GIF (alpha transparency) and is not patent-encumbered,
I am surprised it hasn't surpassed GIF (at least for static images, MNG is needed for animations).
PNG could make websites look extremely good - compare
this demo between Mozilla and IE. The shadow of the bird moves as you drag it around the screen. This was done in 2000 and supported by Mozilla M17 (before 1.0) and later as well as Netscape 6.
Just think how good websites would look now if PNG alpha transparency was supported by IE.