Adds colored borders to Gelbooru.com gallery search pages to show any images you have already viewed. Also shows which images are animated.
Default colors: very light blue for unvisited, green for visited, yellow for unvisited animated gif or png, purple for visited animated gif or png, a less offensive shade of blue from the default for unvisited webm, and red for visited webm. You can customize these with the variables at the top of the script. Animated gif/png highlighting will only work if the image has been tagged as such, since unlike with webm there is no real way to tell them apart otherwise.
Note: Clearing your browser data will clear these, because this script modifies your browser's standard history to store the canonical URL of each image. It never collects or stores any data itself.
This will not work on other Boorus, because the implementation is specifically tied to things that are unique to Gelbooru.