This userstyle fixed the white flash problem in Firefox for me: https://userstyles.org/styles/44928/dark-grey-firefox-about-blank-about-newtab https://userstyle

This userstyle fixed the white flash problem in Firefox for me: https://userstyles.org/styles/44928/dark-grey-firefox-about-blank-about-newtab https://userstyles.org/styles/44928/dark-grey-firefox-about-...