Hey, that's not quite true. ;-)
I wrote most of our javascript on firefox. My firefox has no add-ons except the Firebug. Could it be one of your extensions? Have you tried refreshing it? Which version/OS?
We use howler.js to play the sounds. I have to say that I was a bit surprised to find Chrome/Safari/IE can play mp3 but Firefox plays ogg. I even had to submit a patch[1] so that howler.js can work on firefox under some weird edge cases.