Keep an offline image thumbnail of each page tab (reasonable image quality) to be shown when the mouse is over a tab

Keep an offline image thumbnail of the page tab (reasonable image quality) to be shown when the mouse is over a tab.
In order to make this feature more user friendly could be added a tab button, so when the mouse pointer is over this button it shows the thumbnail. Or it can just shows the thumbnail of the tab where the mouse is over at.. In my opinion this would be very handy..