New Identity may temporarily leak state
While booking tickets to the dev meeting via https://www.kayak.com, I hit New Identity and went back to the booking site immediately, and my destination city was filled in for me in the departure field. This seems a bit odd, especially since it also did not list my departure city in the destination field, or seem to have any other itinerary information from my previous search. Unfortunately, I don't know which exit I was using, but the site also does not normally fill in the departure field for you. Attempts to reproduce the issue also failed.
I don't believe I ever typed in the destination city in the departure field either, and browser.formfill.enable is still set to false. My TBB was storing history, though.
I did have popup windows open, so this may also be a manifestation of #5309 (moved) instead of a race condition. I was unable to get it to happen again with other popups, though. New Identity did take a while to close all of my windows in the case where it happened.
There was also a report via email of a twitter account being linked after New Identity some time back that may have been this same issue, or possibly also #5309 (moved). I believe we were unable to reproduce that one as well though.