I know this problem.
I'm on 64studio (debian). I tried this and that but the only thing which was
statisfying was a 32bit Firefox. I found a Ubuntu-tutorial, which works for Debian64,
which describes how you can install 32bit Firefox without using a chroot enviroment. I
actually don't know where it is. Maybe It was in German.
But its easy to install, easy to use and its just one programm.
you can run 64bit firefox and use nspluginwrapper to run the 32bit flash
http://gwenole.beauchesne.info//en/projects/nspluginwrapper
You also have to set the 32bit emulation in the kernel. If you have
gentoo, here's some instructions. If not, it'll give you the way to do
it.
http://gentoo-wiki.com/HOWTO_Flash_9_and_Firefox