I eliminated Firefox animations with a custom userChrome.css file. They are all gone.
/* No blue swipe on tabs when loaded */
.tabbrowser-tab .tab-loading-burst {
display: none !important;
}
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.