The User Agent Switcher extension is no longer actively maintained and is not compatible with the new extension framework in Firefox 57+. The User Agent Switcher extension adds a menu and a toolbar button to switch the user agent of a browser. The extension is available for Firefox and will run on any platform that this browser supports including Windows, macOS and Linux.
![User Agent Switcher Extension](https://cdn-ak-scissors.b.st-hatena.com/image/square/e016323c0111aaa731387ad4fd1948d5fd4c5633/height=288;version=1;width=512/https%3A%2F%2Fcdn2.chrispederick.net%2Fimg%2F2023.7%2Fwork%2Fuser-agent-switcher%2Fmenu-1200.png)