Privacy: To use the “Single tab only” option, the user must grant the permission for the extension to use their browsing history. The permission is needed for checking if the current window already contains open Gmail tabs, so that the extension can open a new tab only if needed. The permission is never used for any other purpose. The extension can be used without the permission, but then the option won’t work.
(This extension is not affiliated with Google. “Gmail” is a trademark of Google LLC.)