How can I give selected roles the ability to edit just their own comments?
Granting 'edit own forum topics' on the Permissions page only gives the ability to edit the original topic - not replies (comments) to that topic.
Granting 'Edit posts' on the Access control tab of a specific Forum gives permission to edit all posts - not just the User's own posts. This is only suitable for an administrator.
Comments
Comment #1
salvisUsers can edit their own comments as long as no one has replied to them.
This is a feature of Drupal core that was broken in FA 6.x-1.7, but has been fixed in the -dev version, as you can see in the CHANGELOG.txt.
Editing own comments past that point is not supported. It may be implemented in the D7 version at some point, but probably not in the D6 version, unless someone volunteers to do all the work.