I assume by "Joe" you mean @joe.farage's script, but I only know that because I tend to read almost every post that comes through here. In the future, it would be helpful to include a link to the thread with the script, or post the script itself, or something to help people know what you're referring to. Or alternately use the @ tag in the post to make sure the script originator is notified of the thread.
I have not looked at his script recently, but I can tell you that not long ago Mozilla stopped including a path directly to their latest full Firefox release from their FTP site. If you navigate now to "Latest" you see a text file that has instructions on how to obtain the latest release, not an actual download DMG. Its still possible to script downloading the latest version and even getting the latest version number, but if his previous script is still using the older FTP URL, it won't work anymore until its reworked to accommodate the changes from Mozilla.
For reference, this is the URL to get the latest en-US language release of Firefox:
https://download.mozilla.org/?product=firefox-latest&os=osx&lang=en-US
You can change the lang=en-US to get other languages, but I'm not sure of the exact strings to use. I think the text file in their FTP site mentions it though.
Maybe you can modify the script to use that link instead of what's in there now.