I'm trying to use a:visited img in a userstyle for YouTube, but it has no effect:
a:visited img {
    filter: grayscale(100%) !important;
}
On the other hand, if I instead use a:visited and a img, they work fine:
a:visited {
    color: red !important;
}
a img {
    filter: grayscale(100%) !important;
}
Why doesn't a:visited img work?
 
    