What exactly is "Flame and Frost"
Delayed answer here, but basically:
Flame and Frost is an ongoing story arc happening for the next month or two. The events contained in it happen in parallel to your personal story (there’s been a blog post in which ArenaNet discuss the implications of designing this content to be capable of coinciding with any level of progress in the personal story). It has no direct connection or dependence on personal story, but the missions are activated in a similar way. You can start the missions regardless of where your personal story is, and the Flame and Frost missions won’t prevent you from accessing personal story content once started.
It’s as yet uncertain if the missions will be available forever; we’ve been told that some things introduced by Living Story arcs will have a permanent impact on the game (such as Southsun Cove) and some will eventually disappear and become part of the world’s history (such as Southsun Cove’s Ancient Karka, or the xmas/halloween events). I personally believe, though it’s not verified, that the missions and events added during these patches will remain in the future, but the minor features like refugees, lost items and dead drops will likely disappear once this arc is wrapped up.
This forum thread contains a rough description of all of the current features of the Flame and Frost living story additions; if you open up the spoiler tag it gives instructions for each new feature.