A very cleaned-up style for the User Interface only. Inspired by Material design, Outlook and Postbox. Affects the main-interface and the calendar/lightning add-on. Detailed description and comments inside the CSS. Please read the additional information here, or the one inside the code. Updated (1) 15.Dec.2015 - force white titlebar also with cuxtom visual styles.
For people who use the awesome Numix Dark theme for Linux. This userstyle fixes Thunderbird's horrible appearance if you use Numix Dark. If you want to know what parts of Thunderbird are changed: Screenshots speak louder than words, so check them out.
Dark theme for Thunderbirds main UI. If you have any issues with this style, please open a ticket at https://github.com/NiklasGollenstede/stylish
Thunderbird tabs without curves and gradients
A dark view of thnderbird conversation, for use with a dark theme On the screenshot, I also use accountColor
Some Opera-inspired adjustments of a particular "square tab" theme to fit with Windows 10 better.
Gets Thunderbird more fit with Windows 8 and Windows 10 looks - sharper tabs, fewer gradients. Customizable.
Makes Thunderbird conform to the system theme for the tab bar and tool bars, removing Australis look. Tabs are taken from Thunderbird 5+ GTK Tabs, which also has an option for native toolbars but it doesn't work well with recent Thunderbird.
A tab style for Thunderbird based on the Numix GTK Theme (http://numixproject.org) and on Numix for Firefox. Changes tab toolbar and tab appearance.
A remix of Thunderbird Darkning by BastienHo.