Open in Private Mode is an addon that enables you to open the current tab (active) in a private window.
Simply click on the toolbar button to open the private (or incognito) window. You can also use the context-menu item (right-click) to open the private window. Please note that, if you right-click on a link, the new private window will have the link URL instead of the tab. Moreover, you can use keyboard shortcut (Alt + Shift + S) to open the active tab in a private window.
In order to report bugs, please fill the bug report form in the addon's homepage (http://mybrowseraddon.com/open-in-private-mode.html).