Why won't this JavaScript work in FF4?

My custom implementation of the Yahoo Media Player works great in all the major browsers. Except for Fi开发者_如何转开发refox 4.

I've tried to use Firebug and the debugging tools in Firefox, but I can't see any errors. It's like the file isn't even executing.

Please refer to the play buttons on any of the following sites (same implementation):

• http://lizebeekman.co.za/lullabies.html
• http://RhythmMusicStore.com/store/ (I know the coding is old and horrible)
• http://rock.co.za/files/top40_sa_rock_legends.html

If you can point me in the right direction, I would appreciate it. Right now, I have no idea where the error is. Instructions for how to spot the error using FF's debugging tools would also be helpful.