Alt Tab Mod: Always Show Thumbnails
GNOME Shell extension. Supports GNOME Shell 3.6.
Default Alt+Tab behavior is to wait around half a second before showing window thumbnails or not to show thumbnails at all for single window applications. This extension forces Alt+Tab popup to always show window thumbnails of the selected app. This way you can always preview the window you are jumping to.
OBS: not guaranteed to work together with other extensions that also modify Alt+Tab popup. Tested only with 'Alt Tab Workspace'  and other 'Alt Tab Mod: ...'.