Pane and menu fonts

This article was written for Thunderbird but also applies to Mozilla Suite / SeaMonkey (though some menu sequences may differ).

You can change the font, font size, and other attributes of fonts used in the folder pane, message-list pane, menus, and elsewhere in the user interface (UI). To do so, add the relevant code shown below into your userChrome.css file, making adjustments as desired to suit your own font preferences.

Global UI font

Use the following to change the font everywhere in the user interface—folder pane, message-list pane, menus, dialogs, toolbar buttons, etc.

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

Note that other code in your userChrome.css file may override the above.

Fonts for specific UI elements

Instead of changing the font globally, throughout the user interface, you can change it for only specific elements. Below are examples.

Trees

Trees contain the lists of items that form the main part of Thunderbird's user interface—the folders, the message threads, the address books, the cards in an address book. You can change the font for all the trees with one rule:

treechildren {font-size: 12px; font-family: Arial;}

Or you can change individual trees:

#folderTree > treechildren {font-size: 12px; font-family: Arial;}
#threadTree > treechildren {font-size: 12px; font-family: Arial;}
#dirTree > treechildren {font-size: 12px; font-family: Arial;}
#abResultsTree > treechildren {font-size: 12px; font-family: Arial;}

Menus

Use the following to change the font for all menus.

/* Menu font */
menu, menulist, menuitem { 
  font-family: Times New Roman !important; 
  font-size: 12pt !important;
}

Further adjustments

There are innumerable ways you can fine-tune the fonts used in various parts of Thunderbird. For example, you can have separate font settings for the message-list pane and the folder pane, or add colors and background colors to specific elements. See these forum threads for a few examples: [1] [2] [3] [4].