Green’s Dictionary of Slang

(US) a general intensifier, complete, absolute, total, utter.

1824		Woodstock (VT) Observer 24 Feb. n.p.: Whate’er joe fir’d racket they keep up.
1835		D.P. Thompson Adventures of Timothy Peacock 168: I have lately found out a most Jo-fired discovery.
1846		Durivage & Burnham Stray Subjects (1848) 50: He […] always know’d Badger was a jo-fired fool.
1853		‘Philip Paxton’ A Stray Yankee in Texas 219: The jo-fired mean whelp wouldn’t stake me.
2000		(con. 1886) A. De Wolfe Always Her Hero n.p.: I’m gonna march down the street and see what’s so jo-fired important that Michael’s been holed up in his doctor’s office like a bear.