Comment 23 for bug 248271

Thanks Joe, here are my results. The "new" Throbber inside Fx3:

chrome://global/skin/icons/loading_16.png:
$ top
[...]
13078 user 20 0 302m 170m 28m R 20.8 17.0 38:09.22 firefox
 5568 root 20 0 261m 41m 9488 S 13.9 4.2 20:32.95 Xorg

The old one

chrome://global/skin/throbber/Throbber-small.gif:
$ top
[...]
 5568 root 20 0 261m 41m 9488 S 6.0 4.2 20:44.18 Xorg
13078 user 20 0 302m 170m 28m S 5.6 17.0 38:24.30 firefox

And the throbber from attachment of Comment #15

$ top
[...]
 5568 root 20 0 261m 41m 9488 S 5.0 4.2 20:48.42 Xorg
13078 user 20 0 302m 170m 28m S 4.6 17.0 38:28.62 firefox

So it's not APNG which causes the load. It's the more elaborated throbber...