When you click the link to download and end up with a page of random garble, go to "File > Save As." Change the type of file to "All Files," and change the file's name so that it ends with ".mp3".Unless you don't end up with a page of random garble when you click the link, in which case you should've been more specific than, "It wont let me download."
-----Edit-----
Scratch that, I tried it and it turns out that trying to render over 6 MB's worth of text causes Firefox to lock up.
So instead of directly clicking the link to download, right-click it and choose "Save As." Then change the type of file either to "All Files" or just blank, and change the file's name so that it ends with ".mp3".