Tab Shortcuts by PaganCode QWERTY is a great, lightweight, and elegant utility. By pressing the shortcuts, you'll be able to close other tabs or duplicate tabs in the current window in your browser.

Here's a brief overview of the features that this extension has to offer:

It doesn’t need to run in the background and it won’t drain your battery.

It doesn’t require any special permissions.

The shortcut keys won’t clash with any other default keyboard shortcuts, but it provides convenience at the same time.

You won’t have to press the F12 key to access the context menu.

Unlike some other solutions available in the Web Store, these will always execute the action and never fail (regardless of whether the content of the active page has already been fully loaded or not).