Push My Tabs by Pengusto

Push My Tabs gives browser-managed arrow-key shortcuts a direction that matches your tab layout.

• Switch to the previous or next tab.
• Move the active tab backward or forward.
• Follow horizontal or vertical tabs automatically, or force either layout.
• Choose a built-in preset or create one custom mapping.
• Optionally wrap tab switching at the first and last tab.

Firefox reads the browser's official vertical-tabs setting, so Automatic mode follows the actual tab layout.

Push My Tabs is free, advertising-free, local-only, and open source under the MIT License. It has no accounts, analytics, telemetry, remote code, host permissions, or content scripts. Only extension settings are stored in local browser storage.

Support: https://github.com/pengusto/push-my-tabs/issues