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My userChrome.css for Thunderbird

Author: AlexVie
Title: My thunderbird userChrome modifications
Language: en-US
Created: 01:33 on Wednesday, 18. October 2017
Modified: 21:30 on Saturday, 18. August 2018

A small userChrome.css File to change some visual aspects of Mozilla Thunderbird. Works with TB version 52 or later (tested, may also work with older versions)

Available as public gist on GitHub.

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Last modified:
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01:33 | by AlexVie
Reading time: approx. 1 minute(s).


This has been updated for Thunderbird 60 which has been released recently. Do not use it for older versions of TB, it may break your layout.

Even though there are many alternatives today, I still use Thunderbird as my personal e-mail client of choice. While it does have its own set of problems, it’s still one of the best remaining desktop e-email applications in terms of flexibility, security and user experience. It is also free and Open Source and enjoys a huge community.

Thunderbird 60 screenshot
Thunderbird 60 screenshot
Thunderbird 60 screenshot

Since I’m quite picky when it comes to UI design, I’ve made a few changes that improve the look of Thunderbird. Nothing spectacular, just a couple of minor changes:

  • alternating colors for the folder- and message tree control
  • rectangular tabs, less padding, less waste of space
  • minor changes to the message preview- and header area.
  • includes some minor styling changes for the Thunderbird-Conversations add-on.

Here is the code (embedded gist, if that does not show up for some reason, the public gist is available on GitHub.

To install

  • find your TB profile directory.

  • If it does not already exist, create a new directory in your profile and name it chrome (all lower case).

  • Copy the userChrome.css that you’ll find inside the .ZIP you downloaded from GitHub into that freshly created directory. Under Linux, the case matters, the C must be capital, the extension lower case. The folder chrome must be all lowercase.

To activate it, you have to restart Thunderbird. If anything goes wrong and TB looks strange, you can simply remove that file from its folder. It does not change anything outside itself. No special settings are required and the modification is only tested on Thunderbird 52 or newer under Windows.

Compatibility notes

This was initially written for Thunderbird on Windows, but it should work on Linux or OS X. You may want to change the fonts, unless you have Verdana installed on Linux, which is entirely possible but beyond the scope of this document.

If unsure, use sans for the font, this will usually be a shortcut for your default UI desktop font on most Linux distributions.