All-fired means completely, or very much — but only when you think the quality has gone too far. Don't be so all-fired sure: you are far too sure of yourself. It is old American talk, a bit country, a bit sharp, sometimes a bit funny. Younger people almost never say it now; it lives in old stories and in a few older speakers. It can sit before a describing word (all-fired stubborn) or work like a how-word (all-fired quickly). People probably said it instead of hell-fired, so it would sound less rude — a softer stand-in for a curse. Though actually it still carries a little heat: you are not calmly saying very; you are a bit fed up with how extreme the thing is. It is not about losing a job, and it is not the same as fired up (excited and ready).