To try the thousands of add-ons available here, download Mozilla Firefox, a fast, free way to surf the Web!
CloseWelcome to Firefox Add-ons.
Choose from thousands of extra features and styles to make Firefox your own.
CloseReview for User Agent Changer by avada
Rated 4 out of 5 stars
This would be really could if the addon could browse useragentstring.com, to load UA strings from there. Because that site has up to date user agent strings.
Or an autoload a constantly updated xml list would be about as good too. But I don't know of any such lists...
To create your own collections, you must have a Mozilla Add-ons account.