First, expand your page tabs. Then move your mouse cursor to the very right
edge of the vertical scroll bar, just over that line between the tabs and the
scroll bar. The mouse will change to a symbol with two arrows pointing left
and right (it looks like what you would see in an elevator, on the button to
"open elevator door").
Anyway, when you get that symbol click and drag to make your page tabs
bigger and smaller when "expanded."