So I've been taking a break from the game and when I started up today, I noticed that sometimes when I'm at a questgiver, I see a little note under the quest description panel that says 1(or 2) Breadcrumbs available.
the thing is, that image shows that the "breadcrumb" is actually a quest, The Night Watch, which I'd alread accepted and which had nothing to do with Abercrombie, who is the guy I was talking to when this notice popped up.
I tried googling but my fu was weak. Is this something new in the game? What is it a mod? What is it trying to say about the Night Watch quest?
Breadcrumb quests are quests that lead you to a certai quest(-hub), but arn't required to start the quest-chain/hub.
On the other hand, if you start the quest-line without the breadcrumb quest you "loose" one quests, as this will be marked as unavailable. :D
You could also post a list of your installed addons, or disable any quest-related addons you have and see if the text goes away. I haven't seen any such window, and betwee the quest's internal ID number being shown in it, and the textures being stretched to larger than their intended size, it's definitely not part of the default UI.
Aha! It turns out that the breadcrumb feature is now part of the Quest Completist mod. Thanks everyone for your advice.
Here's the description from the mod notes:
New Breadcrumb Warnings: If you attempt to pick up a quest for which a breadcrumb exists, the addon will check if you have completed that breadcrumb, and if not you will see a warning appear below the in-game quest dialog giving you details of the quest you have missed.