1870, "a rustling," from French (19c.), possibly imitative of the rustling of a dress. Meaning "fussy details" is from 1876.
Examples from the Web for frou-frou
And she went out, and I heard by the frou-frou of her skirts that she was ascending the stairs.The Czar's Spy|William Le Queux
The frou-frou of skirts, the delicate mysteries of the toilette, will cease to thrill any but the very young men.What is Coming?|H. G. Wells
No people in their right senses could have accepted my "Frou-Frou" instead of Sarah's.The Story of My Life|Ellen Terry
But before we left him he insisted that we should sit through his favourite "Frou-Frou."Poor Folk in Spain|Jan Gordon
It is not Frou-frou that Molière would have handed down to other generations in enduring ridicule, had he been living now.