Random User-Agent is an application or website that can automatically change your browser’s user-agent string, allowing you to browse the web anonymously. By spoofing your user-agent string, you can appear as if you are using a different type of web browser or device than you actually are. This can help you hide your identity, bypass geo-restrictions, and avoid being tracked by advertisers, search engines, and other websites. Random User-Agent also helps to protect your privacy by preventing websites from collecting your personal data or tracking your online activities. Additionally, it can help you to identify different types of malicious software or websites.
Privacy Possum
Chameleon WebExtension
User-Agent Switcher
Man in the Middle
Chameleon is a very good add-on. It has many options and the GUI is easy to use. It is open source and therefore transient. A very nice feature also is that it allows a fake/random user agent to be "fixed" and not rotated every time or at set intervals. Many user agents, such as Random User Agent, "do not" allow you to set a fixed fake user agent, and changing user agents can be less unique and stand out. It does what it says very well.