I'm frequently finding that media is auto-playing on sites even though I have plugins.click_to_play set to true and media.autoplay.enable set to false. I'm pretty sure this is an issue with HTML5 media. Long ago I disabled Flash and uninstalled Java. The only two plug-ins that are enabled in my profile are: 1) OpenH264 Video Codec provided by Cisco Systems, Inc. 2) Primetime Content Decryption Module provided by Adobe Systems, Incorporated 11 Whether media on a webpage plays or not needs to be 100% controlled by the user and this setting needs to be easy to configure. More and more sites are trying to force their media content onto unsuspecting users with no way to pause or stop said content.

It appears Bug 659285 addresses my issue.