I always got the following problem when trying to start the firefox-bin:
./firefox-bin: error while loading shared libraries: libgtk-x11-2.0.so.0: cannot open shared object file: No such file or directory
And finally I found the magic hint which helped:
sudo apt-get install ia32-libs
As the firefox binary of the beta is a 32 Bit one, you will need the compatibility thing for 32Bit, so install the ia32-libs and the problem is gone.