User-Agent JS Fixer

This addon can change the JavaScript User-Agent on a per-site basis, rather than changing for the whole session.
It does nothing by itself, but it complements the functionality of another addon like UAControl or ua-site-switch. No additional configuration is required, it uses the same settings from them.

All it does is to redefine the User-Agent for JavaScript code (navigator.userAgent) using the same string that was sent on the HTTP header.

NOTE:
Any website where you enable javascript can see right through your fake because this add-on does not cover the navigator.oscpu part of the user agent.