Change keyboard shortcuts for previous and next tabs

You are not missing a setting. Firefox now has customizable shortcuts through about:keyboard, but Previous Tab and Next Tab are currently not exposed there as customizable actions. Mozilla's own documentation lists the customizable-shortcut feature, while a current Mozilla Connect request specifically asks for these two actions to be added. For now, you have these options: Use the built-in shortcuts: Next tab: Ctrl + Page Down Previous tab: Ctrl + Page Up If you want Ctrl + Alt + Left/Right, Firefox currently doesn't provide a built-in setting to assign those keys to previous/next tab. You can check your available customizable shortcuts by typing about:keyboard in the address bar. If you search for “tab”, you'll see the actions Firefox currently allows you to customize. If you specifically want custom keys such as Ctrl + Alt + Left and Ctrl + Alt + Right, you'd need to use an extension or an external keyboard-remapping tool. So the short answer is: yes, this is currently a limitation in Firefox, not something you're overlooking. Mozilla is already tracking a request to add customizable Previous Tab and Next Tab actions.