Firefox new tab light/dark mode

userContent.css

/* create this as /chrome/userContent.css under Firefox Profile directory */

/* Enable Light/Dark Mode New Tab Background Color */

@media (prefers-color-scheme: dark) {
    @-moz-document url("about:newtab"), url("about:home") {
        body { background-color: #222 !important;}
    }
}
    
@media (prefers-color-scheme: light) {
    @-moz-document url("about:newtab"), url("about:home") {
        body { background-color: #ddd !important;}
    }
}