I'm using the behavior Play Sound in an image map.
In IE everything works fine, but I do not hear any sound in FireFox.
What can I do to solve this?
Short answer: Don't use sounds on web pages.
Long answer: You and your site visitors need to install a plug-in for your browser so it can recognize the sound file and launch a helper application to play it. In most cases, this method fails to work because most people aren't willing to install extra plug-ins just to support your site.
Flash is more reliable for this as most people have a Flash Player already installed on their system. But again, gratuitous music and sound effects aren't for everyone. People with co-workers in the next cubicle, a sleeping baby in the next room or who surf while listening to CDs and web radio, may not appreciate your noise. Rethink the need for this.