Theymos disabled it.
I just disabled marquee board-wide. I don't see any use for it.
I did not know it.

I am not surprised that theymos disabled it because the head admin is like an old-school man, and he is uncomfortable with animated things. LoyceV pointed that the head admin disabled animated avatars because he felt it is annoying experience.
Here is his announcement.
OK, APNGs are now detected. Old ones are grandfathered for now, in part because people have ongoing campaigns, but in the future I might (or might not) go through and remove them.
It is time to add this change into
Bitcointalk's important historic changes.