Firefox does have an official 64 bit release for Linux since a while:
ftp://ftp.mozilla.org/pub/firefox/releases/16.0.1/linux-x86_64/
ftp://ftp.mozilla.org/pub/firefox/releases/16.0.1/linux-x86_64/
Will try this later, as I had to install several 32-bit libs to use the 32-bit version on Fedora 64-bit