In a previous life I did a bit of XUL Firefox add-on development so I thought I'd take a quick peek at the Revert Site add-on: Revert Site by steeev+
I concur. As of v1.2.2, for Windows, it appears to set the User Agent to:
Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2661.102 Safari/537.36
This is set in background.js starting at line 102: // Switch User Agent ... the Windows NT 10.0 bit is hard-coded. I'm guessing you could probably substitute your favourite OS.
There is also this small CSS tweak:
div.fbPageBanner {display:none}
This hides the "To help personalise content, tailor and measure ads and provide a safer experience, we use cookies. By clicking on or navigating the site, you agree to allow us to collect information on and off Facebook through cookies. Learn more, including about available controls: Cookie Policy." ... which to my mind should really say: remember to clear all Facebook cookies once you're done!
Disclaimer: I don't use Facebook
Ben.