1. Make the <profile>/chrome directory if it doesn't already exist.
2. Clone the repository inside that directory.
3. If you already have a userChrome.css file, move it into the userChrome.css.d directory UNDER A DIFFERENT FILENAME.
4. Run make inside userChrome.css.d.
5. Symlink userChrome.css.d into the chrome directory.

Also included is a Tree Style Tab stylesheet at _tst.css. To use it with the WebExtension version of TST, simply paste it into the "Extra style rules for sidebar contents" text box in the Advanced section of TST's preferences and select the "Vertigo" theme.

Whenever you add, change, or remove a stylesheet, restart the browser. If you added or removed stylesheets, run make first.

The generated userChrome.css file is just a list of @imports. Therefore, you only need to run make when adding or removing stylesheets.