Hey, I had the same missing toolbar icons problem as described in this thread, and i also had the same problem downloading the PHP attachment. I tried three different methods,
1) download it with DownThemAll download manager
2) download with the regular firefox download manager
3) download it with right-click & "save link as..:"
and the first two methods always ended up with concatenated files, 4 out of 4 tries.
Method 3 worked immediately.
I have never had this problem before.
funny!
However, having checked that all files end with ?> now I'm all patched up and happy again.