Pane and menu fonts

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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 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;}


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;

Points vs. pixels

Note that these examples specify the font sizes in either points (pt) or pixels (px). The difference is that point sizes will be converted to pixels for display based on the screen resolution. Thus, at the default 96dpi, the 12pt font corresponds to a 16px font. In operating systems other than Windows, the screen resolution may depend on the value of layout.css.dpi. Most of the pane and menu fonts in the default themes are specified in points rather than pixels and therefore subject to that scaling.

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].

See Also