When people show images on the web about the new Firefox, that is Firefox ≥ 4, there is almost always this bright orange button in the upper left corner, that replaces the menu bar and moves the tabs to the window frame:
I’m using Firefox under Ubuntu and Windows XP, so I thought, that it might have to do with Windows XP’s age, that there is this feature missing.
However it turns out, that the explanation is way simpler: Firefox simply doesn’t mess around with your old configuration when upgrading. So to come from the default view
to the view with button, you have to deactivate the menu bar:
You can either go to View > Toolbars > Menu Bar in the menu bar and click there or you click right in an empty area of any of the tool bars and remove the check mark from menu bar.
As it turns out, I’m by no means the first to find this out, but I did so on my own ;-).