It is an expression that my mother uses when someone does something that she feels is particularly dumb.

"Your 16 year old son is sleeping with a 21 year old stripper"

"Well, shit fire and save matches!"

This is translated in the few dictionaries I have seen translating colloquial expressions as roughly meaning "damn".

I feel that the phrase means more than that. It seems to be a good admonishment, at least the way my mother used it. Even if your act is astounding, possibly even magical, your method could bring you a lot of pain. If you compared it to the ordinary things you could do to accomplish the same, you'd see it.

It seems that it was once a fairly common exclamation in East Texas, but everyone that I say it around now acts like I am crazy.