As a matter of fact. this buttons along with the awesome bar became the main distinguishing factor of Firefox 3.
But Firefox 3 for Linux was a bit out of fashion. This happened since it used the default native GTK widgets. It looked exactly similar to other GTK applications running on board and that isn’t something that everyone will call a slick UI.
People who long wanted to have Windows like Back and Forward buttons in Ubuntu Linux can now rejoice, because the Strata Human Firefox theme does just that. This is what the developers of the theme have to say about it:
This theme gives the clean, glossy look of the XP and Vista "Strata" icons to Ubuntu's Human theme. I took the XP version of Strata and changed the colors in Gimp to better fit the Human theme. I think it fits pretty well.
Bonus tip: This theme works equally well in Windows. Ubuntu fans stuck in Windows during work are gonna love this theme.