Not quite working properly?
Not sure if it's just me, but lately when I use this script, it shows the feed in Google Reader but gives me the message "You are not yet subscribed to this feed" and I have to click the Subscribe button. It used to properly subscribe me. Firefox 3.5.2, Greasemonkey 0.8.20090123.1.
It's working correctly for me here.
Do you get the same problem if you disable the script and try to subscribe to a feed? Maybe something else is causing the problem you're seeing.