Rated 5 out of 5 stars

le CanteburyGhost ar Noll. 23, 2013 · buan-nasc

Great extension that work outof the box on all FF versions (I'm on 26.0) . Also, very nice to see that the developer is working on an update and occasionally answers reviews..For a list of UA's check this one:
http://www.useragentstring.com/pages/useragentstring.php
It covers pretty much every Crawler, Browser, Library out there...