I noticed that the "remove favorite" option doesn't appear. It shows for a micro second when loading the website, but then disappears and only shows the "add favorite/+favorite" button, even on a favorited picture.

It seems to be all working for me, probably your end.

Try clearing browser data, using a different browser or whatever people usually suggest.

Yeah it has happened to me too (though not recently, last time it happen was like a month ago, and it only happened on my android), funny thing is I never did anything to fix it, I just know somehow it got fixed for me...

Well, it works like it should on internet explorer..... For some reason.
So, I guess it is just browser related, which is waterfox that I am using.

Well, then the problem is my own and I guess admins can take down the thread.

Please submit future bugs in the bug report thread :)

I'm gonna go ahead and lock this