The Break Points tab shows you all of the break points that you have set. Break points can be set via the History and Sites tabs as well as the 'Add a custom HTTP break point' button on the top level toolbar

Right clicking on a break point will bring up a menu which will allow you to:

This will bring up the 'Edit break point' dialog which allows you to edit the criteria that defines the break point. Double clicking on the break point will also show this dialog.

This will remove the break point