Setting User Interface Fonts for Firefox and Thunderbird

On high resolution displays the fonts for the user interface components (UI) of both Firefox and Thunderbird are quite small and may be difficult for many users to read. The user can easily change the font sizes for messages in Thunderbird and web pages in Firefox, but there is no way for a regular user to change the user interface font sizes such as the message list and folder panes, as well as menu bar and menu fonts. This can be easily corrected by the system administrator.


Both Firefox and Thunderbird have a directory named chrome as part of their directory structure in your home directory. These are in their respective profile folders for each application. The profile folders look like those in Table 1.

Table 1: The Chrome directory locations
Application Directory
Thunderbird ~/.thunderbird/default/6d6866ke.slt/chrome
Firefox ~/.mozilla/firefox/w9e1ppgb.default/chrome

The random names generated for the profile directories 6d6866ke.slt and w9e1ppgb.default will be different for you or your users.The chrome directories contain files pertaining to the user interface components of these applications. The file you need to change the UI fonts is not present by default. You must create this file and add the specific user configurations desired.

The userChrome.css File

Create the userChrome.css in the chrome directories of the respective applications and add the following code to it.

/* Global UI font */
* { font-size: 11pt !important;
  font-family: Verdana !important;

Note that the same userChrome.css file can be used for both Firefox and Thunderbird for this specific function. You can copy the file you create for Thunderbird to the chrome directory for Firefox or you could create a single file in one chrome directory and a symbolic link to it from the other. Other entries you might make to this file may be specific to one or the other of these programs and might cause problems.



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