These animated .png avatars have certainly become more obvious over the past few days since the Stake.com bounty campaign started paying anyone for any old spam with no max post limit, even with animation_mode set to "once". As suchmoon has said, it must be very distracting having the entire left side of the page play that nonsense over and over.

On a somewhat related note, another pet peeve of mine is autoplaying videos on various webpages. While a good pop up blocker will block many, some inevitably slip through. If you change "media.autoplay.default" from 0 to 1, videos won't play until you click on them.