all forms of BetterJTV, whether script or plugin, calls the script on s3.amazonaws.com, which does the actual work on jtv; I believe that that allows one place to update for all browsers; it also allows web access for the additional emotes, since they can't be packaged easily in a script.
For some reason, this script gets another script from an amazon s3 domain. I don't know why, but frankly I suspect it's because the other script does something nefarious. This is almost certainly malware. Avoid!