User-Agent Switcher and Manager is a versatile extension for Firefox that allows users to modify their browser's user-agent string easily. This feature is particularly useful for viewing mobile versions of websites or for testing web applications under different browser conditions. The extension supports per-site customization, enabling users to set specific user-agent strings for individual domains while also allowing exclusions for others. Additionally, it includes an option to randomize user-agent strings for enhanced privacy and security.

This subscription-based tool employs a two-factor approach to mimic the default user-agent string effectively, ensuring reliable operation without consuming resources when not in use. It is compatible with a wide range of operating systems, including Windows, Mac OS, and various Linux distributions, as well as support for numerous browsers beyond Firefox. Modern identification mechanisms such as Client Hints headers are also supported, making it a robust choice for web developers and privacy-conscious users.