Tell whether video is loaded or not in Javascript

So, I've been using a listener on

document.getElementById("video").buffered.length

to see if it's greater than 0 for when a video's loaded or not. This works for a very small video, and only in Google Chrome. It doesn't work in Firefox at all. Any ideas for how to get this to work?

I essentially want to wait till 3 seperate videos are loaded to take a specific action, how do I go about this?