I have an onboard sound card, and also a connected bluetooth headset. I have configured the bluetooth device in `/etc/asound.conf`:

```
# cat /etc/asound.conf

pcm.bluetooth {
    type bluetooth
    device 12:34:56:78:9a:bc
    profile "auto"
}

ctl.bluetooth {
    type bluetooth
}

```

By default, the onboard card is used for all sound (apparently, the default onboard card does not even need to be listed in asound.conf)

When I want an application to use my bluetooth alsa device, I have to specify it, such as:

```
mplayer -ao alsa:device=bluetooth file.mp3

```

That's fine for me. But I need a way to tell my browsers to use bluetooth alsa device as well.

I have found a way how to start chromium using the `--alsa-output-device` commandline option:

```
chromium --alsa-output-device=bluetooth

```

I need a similar way to start firefox, but I could not find any.

How can I tell firefox to use my bluetooth alsa device, without having to modify `/etc/asound.conf` or `~/.asoundrc` every time ?

UPDATE:
=======

I have followed @lgeorget's advice and my `/etc/asound.conf` now looks like this:

```
pcm.!default {
type plug
slave.pcm {
        @func getenv
        vars [ ALSAPCM ]
        default "hw:0,0"
    }
}

pcm.bluetooth {
    type bluetooth
    device 12:34:56:78:9a:bc
    profile "auto"
}

ctl.bluetooth {
    type bluetooth
}

```

When I start firefox using `ALSAPCM=bluetooth firefox`, I do get sound in my bluetooth headset, but firefox runs at 100% CPU (on my 4 cores) and the youtube video plays at 10x speed (and the sound is correspondingly (garbled). I don't understand what's happening. When I start firefox without `ALSAPCM=bluetooth`, everything is OK, and sound plays on default alsa device.