dumindu

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

:root:-moz-lwtheme-brighttext {
  --chrome-background-color: #424242 !important;
  --chrome-color: #8f8f8f !important;
  --chrome-secondary-background-color: #363636 !important;
  --toolbox-border-bottom-color: #333333 !important;
  --url-and-searchbar-border-color: #333333 !important;
  --focus-ring-box-shadow: #191917 !important;
  --url-and-searchbar-background-color: #363636 !important;

mrkwatz

As far as I am aware the time has come and as of Firefox 72 XUL has been stripped from firefox and so the method used to inject this scrollbar theme is no longer supported -- reference the following for future scroll themes:

Mozilla is currently working to phase out the APIs used to make this theme work. I will try to maintain each version until that time but eventually there will be no workaround. When that time comes there is a new, but more limited api for applying simple themes to scrollbars. In nightly I am currently using the following userContent.css

:root{
	scrollbar-width: thin;
	scrollbar-color: rgb(82, 82, 82) rgb(31, 31, 31);
}