Don't work. Thanks for trying.

Did not stop the videos from playing.

Stops all but the large one at top of a page. Those still load.

I have no idea why the Huffington Post auto-play is so much more tenacious than that of the BBC, but HuffPo stymied all of my about:config fixes. This add on stopped it immediately. Just hope it's not mining my brainwaves for breakfast recipes or making me sterile or anything in the process.