In Xfce, that "Alt-Tab selection icons" feature is called windows preview.
But in this new machine, the tabs I see when I pressed Alt-tab is too big.
The new machine is most likely running Xfce 4.12 for 16.04 release. The older desktop environment Xfce 4.10 did not have this feature, and the newer one Xfce 4.12 has the windows preview. User will see the windows preview only when display compositing is enabled in Xfce.
How can I reduce the size to normal one?
Unfortunately, the size of windows preview is automatic. That is determined by the number of running application windows that can fit within the screen. Given any particular screen size:
- With several running programs, windows preview will appear big
- With few or more running programs, windows preview will appear small
For example, given a laptop that runs Xfce with screen resolution of 1280x800: the windows preview will appear big when switching between 6 or less running programs, and the windows preview will appear small when switching between 7 or more running programs.
User can instead hide the windows preview.
Go to Settings > Window Manager Tweaks > Compositor and uncheck the option for:
- Enable display compositing, or
- Show windows preview in place of icons when cycling
Uncheck option 1 to run Xfce without windows preview and without desktop effects at all. Else, uncheck option 2 to only hide the windows preview, but still have some desktop effects. Either way will work.