By default Gnome 3 "Alt Tab" switches windows on all workspaces.
As I prefer to have many workspaces with little amount of windows on each of them this behaviour does not work for me well.
I want to switch windows on the active workspace only.
After looking at the code on GitHub it turns out that this following command does the trick:
gsettings set org.gnome.shell.app-switcher current-workspace-only true
No extension needed.