Please post the url of your site and post the relevant piece of the html-code you created.
If the code was generated by some html-editor program, also tell which one that was. It could be that program just generates non-standard code, and then you might need to contact the author of that program. If you typed all html involved yourself, you're the only one who can make the necessary changes.
By the way, are you sure it's not a setting in your Firefox to suppress background music? That would be another possible cause for this behavior (I don't know if such a setting exists; in fact, IE has one in Tools>Options>Advanced).
I created a website on geocities.com using IE. Everything works fine when viewing website with IE but I just happened to use Firefox browser and noticed no sounds are heard on any of my html sites where I have background music files. Is it me or is it firefox? Do I have to insert certain html language in order for firefox browsers to hear the sounds?