Comment 0 for bug 248271

I just installed Firefox 3 on an old laptop, and I noticed that the application startup was significantly slower than what it was in Firefox 2 (I had about 20 saved tabs loading on startup). I also noticed that loading new pages was taxing the CPU in a way that Firefox 2 never did--even when Firefox was just waiting for the server to respond (this is before receiving any data, so it couldn't have been the page layout/rendering that was eating up cycles)--which made me suspect the new throbber.

So I decided to test this theory:

1) Type chrome://global/skin/icons/loading_16.png into the urlbar
   Firefox CPU: 55-70%

2) Type chrome://global/skin/throbber/Throbber-small.gif into the urlbar
   Firefox CPU: 15-20%

The new APNG throbber is over 3x more expensive than the old GIF throbber. This probably doesn't amount to much on newer machines, but on this older machine (P3/800), it really bogs things down, especially when there are several of these throbbers spinning at the same time (e.g., when loading saved tabs while restoring a session or loading a folder of bookmarks; in these use cases, Firefox becomes virtually unusable).

I'm not sure what the best solution here would be (or if there even is a good solution). For me personally, I've swapped out the new throbber and replaced it with the old one, but that's not something that most people would know how to do.

I'm also not sure what exactly is the cause of the inefficiency of this throbber--whether it's something with our APNG implementation or something with the throbber itself (alpha blending isn't cheap).