Build ID: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:32.0) Gecko/20100101 Firefox/32.0 It is only possible to dismiss sheets in the new in-content preferences by pressing the esc button. Not all users might know this and some sort of close button should be provided. STR: 1. Go to in-content Preferences on OS X 2. Go to /Security/General/ and click on "Exceptions" 3. There is no way to close the sheet that appeared with the mouse This can be seen in all places that uses sheets in the in-content preferences, like /Security/Passwords/ "Exceptions" button etc