When reviewing edits there is text inviting to improve the edit:
Approve, reject, or improve edits suggested by users. (less)
Approve edits you know are correct
Reject those you know are wrong
Skip if you are not sure and want to go to the next suggested edit
but I see buttons only for approve, reject, and skip. How to improve the edit?
In case it makes a difference: I am using Firefox 16.0.2 (Mozilla Firefox Ubuntu canonical - 1.0)