Autocomplete throbber causes excessive CPU usage on some browsers

This is pretty pathetic on the part of modern browser vendors, considering how long animated GIFs have been around, but both Firefox (v18) and (especially) Chrome (v24) experience excessive CPU usage while on any page with an autocomplete-enabled field. This is most evident when the browser is being displayed on a monitor that's being run by a USB video card (like the EVGA EV+16 attached to my Macbook).

I've discovered that the reason that the CPU usage goes through the roof is because Drupal's autocomplete throbber is an animated GIF. You can't see the animation unless you've typed in a bit of text and the autocomplete ajax code is currently running, but that's just because the animated part of the GIF is being hidden most of the time. Here's the actual GIF:

This isn't entirely Drupal's fault; it's really just that the browser is being extremely inefficient about rendering the throbber. But if it'd be possible to change the throbber so that it's only an animated GIF while the autocomplete code is running (rather than displaying the animated GIF all the time), it would stop some people's browsers from severely degrading their computers' performance while on certain Drupal pages.

For example, my CPU usage goes up to 80%+ while I'm on an issue queue page in Chrome, due to the "Project" field's throbber. Using the Chrome inspector to delete the CSS that puts the throbber into the page instantly drops my CPU usage to normal levels.