I have a Windows 11 PC with Creative Sound Blaster Z sound card. The sound card and Windows settings are configured for 5.1 speakers and both test OK for sending sound to all 5.1 speakers correctly. Additionally, I can go to https://www2.iis.fraunhofer.de/AAC/multichannel.html using Chrome or Edge browsers and all the tests play correctly to all of my 5.1 speakers. However when I go to this same site (or any other with 5.1 audio) using Firefox browser, the 5.1 audio only plays in stereo (no audio to center or rear speakers - everything is down-mixed to the front L/R speakers only). I've double-checked that the Mozilla channel in Windows Volume Mixer is configured correctly (for output to the Creative Sound Blaster Z device), and none of the output audio enhancement modes are enabled in the Sound Blaster control panel. Firefox is version 136.0.4. Bottom Line: only Firefox seems to be having trouble playing 5.1 audio correctly. Any ideas what might be wrong or any settings adjustments to try?