(Tabs on top)
Of course, you don't need to use Windows or Mac to install those two themes, their names only state the way the tabs will look!
Elementary Firefox currently only works with Firefox 3.x, but Firefox 4.x support is expected soon.
Download Elementary for Firefox (once you download it, extract the .zip and you will find the 3 Elementary for Firefox theme variations). Don't forget to also install the Elementary GTK+ theme.
Many thanks to Ubunlog for the news!