This is a good estension because it spoof others navigator values in about config. I found a bug, after choice a browser prefecence do not update the vendor value. Some browser like Google Chrome have a vendor "Google Inc." or Opera Browser have vendor "Opera Software ASA", firefox have vendor empy "". I suggest to add the spoof of vendor like others navigator values. This is one of few estension that really spoof in serious mode because there are many value to change not only useragents to spoof a browser. Take into consideration the idea to change the value of vendor because it is important and some browsers communicate it to the sites to be identified. Have a nice day.

Update 06 December 2018.
1) I found some incorrect value in this estension, I added the complete image of all navigator values for firefox and Google Chrome, please adapt the estension to show correct value because some site can block browser with incorrect navigator data.
https://imgur.com/60y4pBI
https://imgur.com/PYMcFRS

2) There are a bug, when you choice some useragent must be show oscpu null "" otherwise show original os in the machine. The user agent setted show a user agent (in my foto android) but oscpu (in google chrome is always null "") show real os (in my chase windows 7).
ThIs is a bug important to fix because show a conflict of the os from the user agent setted and oscpu grabbed via javascript.
https://imgur.com/jyfmyCk

I look in the estension there are a javascript file to set the navigator to show after choice an user agent, please look the 2 image added to adapt the estension to show correct values, i added image from firefox and google chrome with complete navigator list values.

Thanks your work.