Toggle between your current and last used (focused) tab with a keyboard shortcut (ALT+Q by default) or mouse click on the icon.
This is free software. Please consider a donation: https://www.paypal.me/orschiro
* Should the default keyboard shortcut ALT+Q not work for you, then please type in chrome:extensions in the URL bar and define your own keyboard shortcut under -> Keyboard Shortcuts at the bottom of the page.
* This extension is intentionally kept simple. The only functionality it provides is to switch between two recent tabs. I will not include any other functionality. Sorry!
This extension is to a large extent based on the extension Last Used Tab Switcher (Alt + Q)  but was made compatible with recent Chrome versions and fixes the bug that the default keyboard shortcut ALT+Q was not working. Furthermore it provides an alternative to the Recent Tabs extension which was reported to be slow on Linux systems.
You can still assign your own custom keyboard shortcut. For that type in your URL bar chrome:extensions, scroll down and click on 'Configure commands' to define your own shortcut for the extension .
Any feedback is highly appreciated. Write me an email to firstname.lastname@example.org or file a bug report / feature request on Github .