At least the idea was there from the beginning (snoop a little bit in the history of this wiki page if you are interested) when they thought about improving their metrics gathering: https://wiki.mozilla.org/MetricsDataPing
Interesting is also the related discussion at the bug concerning the client-side implementation: https://bugzilla.mozilla.org/show_bug.cgi?id=718066
Unique ID for every Firefox Installation coming?
Unique ID for every Firefox Installation coming?
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20100101 Firefox/11.0
Re: Unique ID for every Firefox Installation coming?
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.19) Gecko/20110420 SeaMonkey/2.0.14 Pinball NoScript FlashGot AdblockPlus
Mozilla/5.0 (Windows NT 5.1; rv:12.0a2) Gecko/20120206 Firefox/12.0a2 SeaMonkey/2.9a2