Menu items that open in a new window should open in a new tab instead

[scalebearer]

About Firefox, manage history, manage bookmarks, downloads and any other menu items that open in a new window should open in a new tab.

The current behaviour is inconsistent. Some menu items (passwords, add-ons and themes, task manager) open in a new tab, others open in a new window (about Firefox, manage history, manage bookmarks, downloads).