To check if Firefox is 32-bit or 64-bit:

1.) Start Firefox
2.) Open a shell and run the 'ps' command:
  ps -aux | grep firefox
3.) Search the output for 'firefox-bin' which points to the path of the Firefox executable e.g.:
  /usr/lib/firefox-3.6.10/firefox-bin
4.) Pass the absolute path of the 'firefox-bin' file to the 'file' command e.g.:
  file /usr/lib/firefox-3.6.10/firefox-bin

5.) Check the output of the 'file' command, if you see the string 'ELF 32-bit' you'll need the 32-bit Squish package, otherwise the 64-bit package.