Sorry to hear it's not working perfectly... I changed this listing to Experimental. The extension does define keyboard shortcuts via https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json/commands API as seen here https://github.com/qufighter/LastTabz/blob/master/manifest.json#L15 but I'm not sure where you are able to customize them and they are not working yet for me either! I will investigate and may provide a solution to some of the issues in a future update. Thanks for reporting!