remove firefox white flash dark mode

userChrome.css

/*
about:config
toolkit.legacyUserProfileCustomizations.stylesheets: true
create chrome directory in default release path, found in about:profiles
/Users/$user/Library/Application Support/Firefox/Profiles/xxxxx.default-release/chrome
copy userChrome.css and userContent.css to
/Users/$user/Library/Application Support/Firefox/Profiles/xxxxx.default-release/chrome
 */

@-moz-document url(chrome://browser/content/browser.xhtml) {
  #main-window,
  browser[type="content-primary"],
  browser[type="content"],
  tabbrowser#content,
  #content,
  browser[type="content"] > html {
    background: #323234 !important;
  }
}

userContent.css

@charset "utf-8";
/* CSS Document */

@-moz-document url("about:newtab") {
  body {
    background-color: #011326 !important;
  }
}

@-moz-document url(chrome://browser/content/browser.xhtml) {
  browser[type="content-primary"] {
    background: #011326 !important;
  }
}

white-flash.md

Firefox white flash in darkmode (OS X)

• in about:config set

toolkit.legacyUserProfileCustomizations.stylesheets: true

• create chrome directory in default release path, found in about:profiles

/Users/$user/Library/Application Support/Firefox/Profiles/xxxxx.default-release/chrome

• copy userChrome.css and userContent.css to

/Users/$user/Library/Application Support/Firefox/Profiles/xxxxx.default-release/chrome