I have spotted a performance issue which seemed awfully odd at the beginning. On this page at least : http://designshack.net/articles/graphics/design-a-rockin-band-website The page was obviously idle, the blinking ads were disabled with AdBlock. However, the CPU usage remains constant and high (22-35% with xorg-ati drivers, 45-56% CPU with amd proprietary drivers, Radeon 7290 and AMD C70), and is worse when there are images in the viewport. Enabling the repainted areas highlight showed me that every image in the page was constantly redrawn (the full area). I found out that the DOM elements have a .gif background-image (a typical AJAX spinner set with CSS). That is, even if I can't see the animation, Firefox keeps redrawing the entire container and hogs CPU. I don't know what Chrome does, but it correctly considers the area as not to be repainted, and saves CPU. Obviously visiting about:config and setting animation_mode to none sort of fixes the problem. But it's not a real solution. Have I missed something ? Does everyone have the same problem ?