A new version (2.8) of firefox_getLatest has been submitted, though as I won't get around to upgrading to TC13 for a while it's only tested in TC12 (if the missing libXtst dep entry was the only problem with TC13 though, the new version should run just as well).
The new version of the script has a new option "-d" which disables generating the .dep file. This is handy for people who frequently upgrade Firefox and want to keep modifications they've made to the firefox.tcz.dep file (eg. inserting new firefox dependencies like this which the script isn't yet including itself).