I answered this question and it was quickly pointed out that the code in my answer had a few bugs. I deleted it to avoid misleading the OP until I fixed the code and then undeleted it after the correction.
I am not sure if it is relate to the delete-edit-undelete pattern, but after undeleting it the add comment link didn't seem to work anymore. It indicated as clickable, but just did nothing.
Id think the link should still work, or if this is by design get rid of the link.
Did some more troubleshooting:
- The problem occurs on all questions, not just the original one.
- It only happens when I use FF 3.5.3, but not IE7
- It works fine in both browsers on the meta site, just not StackOverflow.