Isn't there a timing which Plot reveals first? Or has that changed? When the first player deceit that Wildfire resolve first Power of blood is useless in my mind.
That was true for awhile, but it is not any longer. Back before Gencon 2008, a clarification was added to the FAQ on plot resolution. Rather than having all plots activate in the order determined by the First Player, plots with constant effects are considered active as soon as they are revealed. The First Player only decides the order of resolution for "when revealed" plots. This is because technically, "when revealed" plot effects are passive effects activated by revealing the plot. Passive effects do not have timing conflicts with constant effects on any other card type, so why did they conflict on plot cards such that the First Player needed to resolve the conflict by deciding the order?
Essentially, the switch made plot cards behave more like every other card type in terms of the resolution of constant, passive and triggered effects (we actually do have plots with triggered effects now).
So, in the Plot phase, say that Power of Blood and Wildfire are revealed at the same time. Power of Blood is a constant effect, so it is active as soon as it is revealed. Nobles cannot be killed. Revealing Wildfire activates its passive "when revealed" kill effect, so that is technically resolved after the plot is revealed (not simultaneously). Therefore, Power of Blood is active when Wildfire is resolved. The two do not conflict, so the First Player has no say in the order of resolution.