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userContent.css in the chrome folder is a CSS file that you can use to change the way web sites and e-mails look. This file does not exist in a new profile. You can create it manually.

Note:  This file only affects your Mozilla application's display (when you are using a particular profile). It does not actually change any web page or e-mail message. For example, if you use the file to change colors in e-mail messages, it does not affect messages that you send—so people who receive messages from you will see them using their own choice of colors, not using your choice of colors.


To create this file manually, use your operating system tools.

Go to your profile folder. Then go to the chrome folder there, creating it if necessary. In the chrome folder, create a plain text file named userContent.css.

To create this file automatically, download the .zip file - Paste the .zip file in your profile folder and unzip/extract it there. A chrome folder will be created with the userContent.css and userChrome.css files already within the folder, together with example files of each.


  • If you have more than one profile, then each of your profiles has a separate userContent.css file.
  • There is another chrome folder where Thunderbird's code is installed. Do not create a userContent.css file there—it will not work.


This file is designed to be manually edited using a text editor. Anything valid in a CSS file is valid in this file. To make the changes take effect, you must restart the application.

For sample styles, see:

Moving and copying

You can move or copy userContent.css to a different profile. If it imports or references other files such as images, then you must also move or copy these other files. To make the changes take effect, you must restart the application.


You can delete userContent.css to get rid of any user styles defined there. To make the change take effect, you must restart the application.

Related files and folders


For some information about common problems, see: Editing configuration – Troubleshooting and Show_hidden_files_and_folders

External links

  • The Stylish extension provides another way of changing styles in web pages and e-mails. It does not use the userContent.css file.
  • The GreaseMonkey extension provides a way to run scripts in web pages.