Safari 6 “Debug” menu: explain choices?
Use Buffered Windows :  
for each window, there will be another window that is off screen. The reason for this is that when the window the user is interacting with needs updating (ie, you move the mouse over the window) the WindowServer simply needs to copy the damaged region from the offscreen window and blast it over to the visible one. Similarly when the content of your window changes, applications are only supposed to update the region that changed. This drawing is performed on the buffer, which then is copied over to the 'visible' window. 
Use Single-process Windows:


puts all open tabs inside a single safari proccess instead of several ones.