Firefox 3.6.8 on Ubuntu 9.10; using TreeStyleTab 0.10.2010040201.
I use the tab-bar on the right, and I would like to see more of the tab names without widening the bar. The default font used is Sans, I believe; I would like to use something like condensed DejaVu Sans. I haven't found anything in the settings, nor in the about:config page, so I presume I can play some .css trick, but I don't know where to start.
How can I do this change?
12 Answers
Install Stylish extension:
Then add this script:
@namespace url(""); .tabbrowser-tabs .tab-text { font-size: 4mm !important; font-family: Condensed DejaVu Sans !important; font-weight: bold !important; color: #ffffff !important; text-shadow: 0 0px 2px rgba(0,0,0,2), 0 0 1px rgba(0, 0, 0,1) !important; } Change options to your linking.
It will look like this:

You can tweak firefox UI fonts, colors etc by editing the userchrome.css file. The process is explained with a long list of snippets for "common" tweaks here. Or if u just want to tweak the font, you can check this is a short tutorial.
As per the official mozilla howto
1Neither userChrome.css nor userContent.css exist by default. If you want them, you create them in the chrome subdirectory underneath the user's profile directory. userChrome.css controls CSS for the UI chrome of the Mozilla application; userContent.css controls CSS for content inside windows.