OK, Google did break their Google player, but I implemented a workaround with JMP3 player, though still keeping the original gmp3 heading to keep the previous MP3 embeds working.

To embed an MP3, while posting click on the gmp3 box and insert the URL of your MP3 file between the gmp3 bbcodes.

Update:

Thanks to EricTheGray's suggestion and resources, the audio player is now HTML5 and no longer flash based.

Firefox seems to not play MP3 in HTML5, so the flash player is also available.

I put back in the JMP3 (flash) audio player alongside GMP3 (HTML5); choice left to the user.

Here's the thread about browser compatibilities with HTML5 and Flash:
http://www.stickist.com/viewtopic.php?f=10&t=5314

JMP3 on top, GMP3 below of Stratocasters:

Thanks, Manny.

I can confirm that the bottom player works on my iOS devices. Firefox seems to be losing it's steam and is going down in popularity. Google Chrome is the cool hotness for now. Both players work in Chrome. Because I don't have Flash installed on my computer, neither player works in Firefox for Mac. On Safari for Mac, the bottom one works.

-Eric

Actually Firefox prefers "open format" file and that's why it manages OGG file for <audio> tag instead of MP3, who is a proprietary format.

I understand their reasons. But the fact is that the web is MP3 and Firefox will either adapt or die. Anyone at Mozilla who thought otherwise is deluding themselves.