I just got a [Cubilux Surround Sound Card (CA7)](https://www.cubilux.com/products/7-1-5-1surround-sound-crad) and reproduced the issue on my MacBook Pro. The channel layout was set to 6 channels: [BackLeft, BackRight, FrontCenter, LowFrequency, FrontLeft, FrontRight]. Chrome works fine, but Firefox doesn't. The mixer wasn't created as I [expected](https://searchfox.org/mozilla-central/rev/b60bff00c0fe136f35e4d6f3316911c090a39f23/third_party/rust/cubeb-coreaudio/src/backend/mixer.rs#184). I suspect the problem is probably caused by the code [here](https://searchfox.org/mozilla-central/rev/b60bff00c0fe136f35e4d6f3316911c090a39f23/third_party/rust/cubeb-coreaudio/src/backend/mod.rs#3874-3899). I'll investigate it tomorrow.
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I just got a [Cubilux Surround Sound Card (CA7)](https://www.cubilux.com/products/7-1-5-1surround-sound-crad) and reproduced the issue on my MacBook Pro. The channel layout was set to 6 channels: [BackLeft, BackRight, FrontCenter, LowFrequency, FrontLeft, FrontRight]. Chrome works fine, but Firefox doesn't. The mixer wasn't created as I [expected](https://searchfox.org/mozilla-central/rev/b60bff00c0fe136f35e4d6f3316911c090a39f23/third_party/rust/cubeb-coreaudio/src/backend/mixer.rs#184). I suspect the problem is probably caused by the code [here](https://searchfox.org/mozilla-central/rev/b60bff00c0fe136f35e4d6f3316911c090a39f23/third_party/rust/cubeb-coreaudio/src/backend/mod.rs#3874-3899). I'll investigate it ASAP.