Give less padding to tabs to fit text in most languages (bug 881434)

This is quick simple fix/hack for https://bugzilla.mozilla.org/show_bug.cgi?id=881434, because it's been bugging me for a while. There are multiple better and cleaner ways to do this, but per comment 1 in that bug, the tabs should be redone, so this is just a stopgap in the meantime.

Here is what it used to look like in english and french (polish and spanish were also affected):
![Original english](http://i.imgur.com/mzryj8C.png)
![Original french](http://i.imgur.com/PybGUQE.png)

Here is what it looks like with that patch
![Patched english](http://i.imgur.com/v4RuJA9.png)
![Patched french](http://i.imgur.com/C1ZwJli.png)