Requested feature overview description.
put a border around favorited posts.
Why would it be useful?
Because its annoying to go into a you want to favorite post to see its already favorited.
What part(s) of the site page(s) are affected?
Post index

My initial though on this is that it would be too expensive to pull up the favorites for the posts and compare them to the current user, but testing would be required to determine if it would scale.

You could instead add -fav:LucarioTheMario to your search and not show any posts you've already favourited.

Tuvalu said:
You could instead add -fav:LucarioTheMario to your search and not show any posts you've already favourited.

Or blacklist fav:lucariothemario here and have them removed for as long as you have it on your blacklist. It'd be easier for the long run, but you'd have to remove it every time you actually want to see your favorites.