Windows Registry Editor Version 5.00

; When clicking the icon of a a running application in the taskbar (that
; currently has multiple windows open), typically a pop-up will appear showing
; the multiple windows, and you'll have to click a second time to select the
; window you want to focus on.
;
; This registry hack instead turns the icon click into a "focus on the last
; active window" action. You can click it repeatedly to cycle focus through all
; the windows open for that application.
;
; With this enabled, the pop-up window display will still show if you hover
; your mouse over the taskbar icon.

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
"LastActiveClick"=dword:00000001