Jonathan Lightner's Historical Dictionary of American Slang (2 volumes so
far; don't hold your breath for P-Z) gives multiple definitions for the word
in question, although I am too delicate to repeat them.  However, the
earliest include:

1598: "Fricciare ... to frig, to wriggle, to tickle."
1786 "Defrauds her wi' a frig or dry-bob."
1811: "Getting boat on the quarter and frigging about all the afternoon."
and, rather late but my favorite:
1922: "It sounded like a pack of skeletons frigging on a tin roof."

(First appearance of "friggin' in the riggin'" is 1957)

Sign me,  Saving Myself for My Wife's House