Random User-Agent for Chrome and Firefox replaces the original browser User-Agent identifier with one that is randomized.

Random User-Agent helps prevent data leakage, and it automatically replaces the user proxy string with a randomly selected string after a specified time period.
Download for Chrome:https://chrome.google.com/webstore/detail/random-user-agent/einpaelgookohagofgnnkcfjbkkgepnp
Download for Firefox:
https://addons.mozilla.org/firefox/downloads/file/4025397/random_user_agent-3.16.0.xpi