If you're using Flash, it takes care of the file format for you. I'm familiar with the ogg/mp3 issue in Firefox. That only pertains to the raw file without a suitable player. As I say, Flash takes care of that for you.
Perhaps your Flash plugin isn't up to date. Perhaps it's something else. But it's not the mp3.
Also I noticed a problem with the external page:
That semi-colon belongs inside the " mark. Or it can be skipped. But having it outside like that is invalid. Such a fine point generally doesn't matter. But when AJAX is involved, sometimes a tiny thing like that can cause some browsers big headaches.
. . . dth:200px;}
<p id="audioplayer_1a">Alte . . .
Anyways, you still haven't told me what the problem is.
What is it?