Mozilla CSS Modifications

Overview

• https://www.userchrome.org/adding-style-recipes-userchrome-css.html

Activate CSS Usage In Thunderbird

Settings/Options/Preferences > Advanced > General > Config Editor > locate the following key:

toolkit.legacyUserProfileCustomizations.stylesheets

Set the above to true by double-clicking on the key.

userChrome.css

Should contain the line:

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);