Blue flash completely destroyed, I confirm it. This is my userChrome.css (I also have a megabar remover in there, that's not shown here): * { transition-

Blue flash completely destroyed, I confirm it. This is my userChrome.css (I also have a megabar remover in there, that's not shown here): * { transition-delay: 0ms !important; /* This is the magic to kill it 100% */ transition-timing-function: steps(1, jump-start) !important; /* Animation Killer */ animation-delay: 0ms !important; animation-duration: 0ms !important; animation-iteration-count: 1 !important; animation-timing-function: steps(1, jump-start) !important; } Also I have ui.PrefersReducedMotion=1 set in about:config.