David Baron reminded me on IRC that there have been throbber design contests in the past…
There’s this Netscape page for a 1995 (?) animation contest (holy 16-color flashback, batman!), which conveniently has images for each frame for the winner and top 5 entries… APNG time!
Here’s the winner (left), and the final version that made it into Netscape:
And the 5 runners up:
There was also a second contest in 1999, but I can’t find the entries anywhere online… These two throbbers are in the old Mozilla 1.7 tree, perhaps they were the winners?
(I love that tile-flipping effect!)