To edit the settings, type in the address bar of the Mozilla Firefox browser:
about:config
Mozilla Firefox browser extension to create, edit and select User_Agent header data:
https://addons.mozilla.org/ru/firefox/search/?platform=windows&q=user-agent-switcher
User Agent Switcher for Google Chrome:
https://chrome.google.com/webstore/search/user%20agent%20switcher/
An example of launching Google Chrome with the -user-agent parameter:
/opt/google/chrome/google-chrome '-user-agent=Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1)'
For Internet Explorer, edit the shortcut, add at the end of the file path:
'-user-agent=Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; en)'
You can check the information issued by the browser on the sites:
whatsmyuseragent.com
panopticlick.eff.org
www.mybrowserinfo.com
etc.