I would love to but don't see a way how to achieve this. From what I can see, I can only add users to roles but can't modify the permissions for a role. Anyhow, I have added you to the contributors. So for you it might be possible now. I will ask Ben about this.

From Ben Walding (The codehaus lead)

This was a bug in the permission scheme!
I've just granted rights for logged in users to edit their own comments.

I'm very reticent to allow any logged-in-user to edit any JIRA. We get
hit by spambots every minute of the day; and allowing them to go in
and hose out issues would make my life painful - and I don't want
that! There is no simple way to revert changes to a JIRA.