How to disable Firefox address bar animation on fullscreen?

How can I disable the address bar hiding animation when going fullscreen in Firefox?

I'm trying to accomplish what this question is about. The solution was to set toolkit.cosmeticAnimations.enabled to false in about:config, but this is not working anymore - the animation returned once I updated to 77 and is still a problem in 78.

EDIT: make sure you set toolkit.legacyUserProfileCustomizations.stylesheets to true in your about:config page before attempting to use custom stylesheets!

You can add the following in your userchrome.css. Learn how to create or edit one here https://www.userchrome.org/how-create-userchrome-css.html

/* To completely disable fullscreen transition */

#navigator-toolbox[fullscreenShouldAnimate] {
    transition: none !important;
}

/* To drastically reduce transition time - zero doesn't work, minimum is 0.01 */

#navigator-toolbox[fullscreenShouldAnimate] {
  transition: .15s !important;
}