Maybe look up "animation" in whatever firewall/security/ad blocker help file you use; a routine update you didn't even think about might have added the feature of stopping animated ads with a blocker that stops all animation (I know ZoneAlarm Pro does this).

You can stop animation at anytime by hitting the escape key; you haven't accidentally or on purpose LOL been doing that somewhere along the way?

And no one changed your Tools>options>advanced/Multimedia "Play animations in web pages"?