Simplifying Firefox download script, fixing bugs, disabling on win/mac.

It's unlikely I'll implement the FF test on win or mac anytime soon, so
I may as well clean up that code. Also the script has broken on Win
because of a Firefox-side change: disabling the script on win/mac for

Review URL:

git-svn-id: 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
1 file changed