Advice needed

I need a license for my new Firefox extension, but I can’t find anything that I like. Here’s what I am looking for:

  • The freedom to run the program for any purpose
  • The freedom to study and modify the program for personal use
  • The freedom to copy the program

I don’t want users to have the freedom to redistribute modified versions of the program, specifically because there are links to stores etc. in it that have my affiliate code in it. When I first distributed BetterSearch to an extension site, it took mere hours for one of the guys to replace the original version with one without my affiliate codes to make it “free”. (Then it took mere hours for me to politely complain, and we’ve come to terms since then.)

So, basically I’m looking for something like the GPL without the part that allows users to spread modified versions of it.

Any suggestions?