Not working on Firefox Mac

Hi there, great stuff you have here. But i have a few problems and i hope you can help me. The default video dooes not start on firefox mac and on safari mac the default video starts 2 times (double sound). Do you know how we can solve the problem?
You can see it here:
http://kemimusic.de/videos
Thanks

http://ww.wp.xz.cn/plugins/cool-video-gallery/