If an entry in the My Bookmarks list is obsolete, then it will be shown with a line through it. For example, instead of ABCDE it will look like
ABCDE. You can manually delete any entry using the button that's in the navigation cluster. But if you have many obsolete entries, you can sweep them away with one click using the button. If the My Bookmarks list has no obsolete entries, then this button will be disabled.