Seems to work for me. I have the newest version of Firefox (3.5.x) and Flash Player. I'm using Windows XP Pro. on an old Dell Optiplex GX270. That's not 64bit, in case you're wondering. Haha.

I had a similar problem with a game project after I added a lot to it, the employer claimed it wasn't working after I added a bunch of high res images into a movieclip. I didn't change much of the code, either. It's just some weird oddity I had to find a workaround for. Now, I use listener management classes for all my event listeners past the loading area. It makes it easier to manage big projects and garbage collection. Yes, you actually have to perform garbage collection yourself in some cases. Suffice to say, my projects always work for me, especially in the test environment ("Test Movie" and "Debug Movie"), so I have no idea why my projects would hang on other systems. It's just weird... and only ever happened once.

This is a shot at nothing, but why are you using underscores in your instance names? I only use underscores to add spacing between words.