Is it possible to get MD5 hashes of all old Firefox executables(not installers) so that i can block them from running for my users?

I do not want to block firefox.exe filename as it will also block newest version, but I can block based on hash. Most convinient would be block firefox.exe except and now provide md5 of the newest ver, but i cannot do that with what i have. The only possibility is to block whole list of MD5s of older Firefox.exe, sadly at mozzilla ftp there are md5's but only for the setups, and i need to block executables from already installed on client machines, not the isntallation packages.