@hearkat: I think Windows Alt+Tab only cares about taskbar instances, whether one application or not. Having, say, two separate firefox windows open is still technically running one application (and one process), but should display as two discrete taskbar instances. In contrast, I think Chrome will combine multiple discrete Chrome processes into a single window, if desired.
For Firefox anyway, cycling between browser tabs can be done in a few ways. Alt+# [1,2,3,4,5,6,7,8,9] switches to the tab. Ctrl+PgUp and Ctrl+PgDn go left and right, respectively. Pretty sure that works on Windows too, but I use GNU/Linux.