I always use Safebooru, but now for some reason, all thumbnails on the list pages have the "blacklisted" class in their <span> tags.
I did a search for other people with this problem, and they had fixed it by clearing their cache/cookies, but that didn't help me. I even tried using a completely different browser, and the thumbnails still don't show up.
As a temporary workaround you can disable javascript. A lot of site functions will still be broken, but at least thumbnails will be visible.
EDIT: To clarify, this is not the usual missing thumbnail bug. The end result is the same, but the cause is different. You'll just have to wait for albert to fix the server.