From before Shakespeare’s “There was a lover and his lass, / With a hey, and a ho, and a hey nonny no”, right down to the present day, nonsense words have been a regular feature of song lyrics. You might think that it’s a stretch to suggest another meaningless la-la lyric filler is the origin of this usefully dismissive word. However, that indeed seems to be its origin, although the usual form until relatively recently was falderal rather than folderol.
There are many traditional rhymes and songs with variants of “fal-de-ral” in them somewhere. For example, Robert Bell noted these words of an old Yorkshire mummer’s play in his Ancient Poems, Ballads and Songs of the Peasantry Of England of 1857: “I hope you’ll prove kind with your money and beer, / We shall come no more near you until the next year. /Fal de ral, lal de lal, etc.” And Sir Walter Scott included a few lines of an old Scottish ballad in The Bride of Lammermoor (1819): “There was a haggis in Dunbar, / Fal de ral, etc. / Mony better and few waur, / Fal de ral, etc.” Charles Dickens had gentle fun with this habit in his Sketches By Boz of 1836-7: “Smuggins, after a considerable quantity of coughing by way of symphony, and a most facetious sniff or two, which afford general delight, sings a comic song, with a fal-de-ral — tol-de-ral chorus at the end of every verse, much longer than the verse itself.”
It was around 1820 that this traditional chorus is first recorded as a term for a gewgaw or flimsy thing that was showy but of no value, though it had to wait until the 1870s before it started to be widely used.