Firefox/Flash vs. Pulseaudio; Audio can't be directed to the desired device

[Jonathan Ryshpan]

Pulseaudio can control which output device receives main audio output
via 

        kmix->Mixer->Settings->Audio Setup->...

which invokes Phonon.  At this point select the audio stream you want to
divert, "Prefer" the device you want to receive the stream to the top
and "Apply".  This sends the audio stream, the output of Amarok (in my
case) to the desired device, "Built-in Audio Analog Stereo" (in my
case).

EXCEPT that this doesn't work for a stream originating in Firefox/Flash.
How can I redirect this stream?  What am I missing?

Many thanks - jon