1. Type about:profiles into your urlbar and go to the page
2. Open the root directory folder specified on the page
3. Inside this folder, create a folder named "chrome"
4. Put the userchrome.css file from this repo into the chrome folder
5. Type about:config into your urlbar and go to the page
6. Paste "toolkit.legacyUserProfileCustomizations.stylesheets" into the bar and set its value to true
7. Go back to about:profiles and click the restart normally buton
8. That should be it!

You have to create the "ui.prefersReducedMotion" config in about:config and give it a value of 1 to prevent some stuttering in the animation.

You have to set "browser.urlbar.openViewOnFocus", and "browser.urlbar.update1" to false in about:config to fix a bug regarding a big white urlbar.