A simple Chrome extension to switch between the two most recently used tabs, with minimal permissions required. There are other extensions with similar functionality, but they often require excessive permissions.
You can install this by visiting Switch Tabs in the Chrome Web Store.
The extension requires Storage permissions to persist the last used tabs across browser restarts.
By default, you can toggle between the two most recently used tabs using
Ctrl-Q (on Mac, Windows, and Linux alike). You can choose a different
keybinding via More Tools -> Extensions -> (Hotdog Menu) Keybindings.