The core of my home studio consist of a Notebook and a firewire mixing console. Unfortunately, Flash used my notebook speakers for audio output instead of the firewire device. There are several workaround setups to circumvent this, but most of them are at least a bit cumbersome.
Thorben Hohn fortunately wrote a library which provides an elegant solution. Here’s what to do:
mkdir libflashsupport-jack
cd libflashsupport-jack
git clone git://repo.or.cz/libflashsupport-jack.git
cd libflashsupport-jack
sh bootstrap.sh
make
make -n install
sudo make install
Restart firefox and listen to your favourite music video on Youtube (Zansa and Bimoya) via jackd – what a joy! All credits to Thorben for the excellent work.

Hi.
Just for the record, there are three ways to run flash on top of jack. First is your approach mentioned above.
Second is via libasound’s jack client as mentioned in http://subversion.ffado.org/wiki/ALSAtoFFADO
Third is simply via Pulseaudio’s module-jack-sink, so you can redirect all your consumer applications (vlc, mplayer, skype, flash, etc.) to jackd. This is probably the most elegant solution, as it allows you to switch your *running* streams from your internal (or USB, bluetooth, whatever) device to your firewire device.
Cheerio