Before there were dozens of decent ad-blocking extensions out there I was a big user of Privoxy. It had an action called "deanimate-gif" that would display only the first frame of the animated image.<p>I'm not sure if Privoxy was downloading the <i>whole</i> image in the background in order to extract the first frame, and I don't know if deanimation used <i>less</i> CPU or RAM than just displaying the animated versions, but I loved the feature regardless.