How do I stop auto play of mp4 files in Firefox?

I’ve recently been working with some mp4 files and given the javascript nature of the links on the system I’ve not been getting the prompt to download but having the files auto playing.

This is rather annoying as Firefox takes a few extra seconds to open up the file and hangs briefly while I need to right click and go to save as and its screwing with my workflow.

All is not lost though so here’s how to make the prompt come up to save as …

(This is correct as of Firefox 50.1.0)

1. Enter about:config into the address bar
2. Click I accept the risk!
3. Into the search field put in media.play
4. Double click “media.play-stand-alone” setting it to false.

You’re done. Test it out and it should be working.