UX is planning to release a special edition of the Whimsy add-on for Firefox's 9th birthday. This meta bug tracks the analysis of Whimsy performance, and any platform + extension improvements required

The majority of the paint time in this profile is spent scaling the images, drawing the borders, a little bit of linear gradient. Just animating unscaled images without any fancy borders or gradients should go very fast.

Okay, so when I show the animated gifs, I'm flipping background-size to "auto" (and background-position to "center"), and I've removed the complicated border with three different colours with some alpha, and replaced it with a single colour with no alpha. Hopefully that'll help a little. I'm not really sure where the linear gradient comes from. As far as I can tell it's not the add-on code. Of course, the border isn't the add-on code either, but that doesn't mean that I can't change/fix it. ;) I would be interested in seeing how much this profile differs from one without the add-on installed, so that I can find out where the add-on is slowing things down.

Blake says we can wontfix this now :)