Firefox: “click to play” for plugin content

Quoting “Opting-in to plugins in Firefox” by Jared Wein:
When plugins.click_to_play is enabled, plugins will require an extra click to activate and start “playing” content. This is an incremental step towards securing our users, reducing memory usage, and opening up the web.
Great feature! I’d love to have this for any kind of animated content. Alas, while it could be done for animated image formats, doing the same for JavaScript-based animations seems impossible.