Based on the details, here are a few things that could be wrong:
- The WAV file might be encoded using an unsupported codec. According to this page about media formats that Firefox supports, WAV files need to be raw PCM data.
- According to the same page, the MIME type needs to be set correctly in order for Firefox to honor the audio file. Either the web browser needs to deliver the correct MIME type, or you need to specify the type attribute in the
<audio>
tag.
Note that the QuickTime plugin should not be in play at any point here.