The tab controls of Netbeans are pretty good, but not when using Joxy. This happens because Netbeans doesn't use a standard Swing component for the tab, but its own component that Joxy doesn't style.
Fortunately in Netbeans 7.2 the option has been added to switch the tab implementation to a normal JTabbedPane, that Joxy does style.
A simple way to do this is the following:
The Netbeans developers, to implement these "multi-row tabs", switch the tabs to a normal JTabbedPane. However you won't get multi-row tabs, since Joxy doesn't support them (since Oxygen also doesn't do that).
Note: this (for some reason) only works for the tabs in the main part of the window (the code editor). The other tabs stay the same. With a lot of messing around with files, I got Netbeans to display all the tabs nicely. However this is such a hack I won't post it here :-) especially as I think there must be a better way (creating a Netbeans module?)