Harold Bloom certainly criticised New Historicism. In his book The Western Canon, he said:
Whatever the convictions of our current New Historicists,
for whom Shakespeare is only a signifier for the social energies of
the English Renaissance, Shakespeare for hundreds of millions
who are not white Europeans is a signifier for their own pathos,
their own sense of identity with the characters that Shakespeare
fleshed out by his language.
and he frequently referred disparagingly to New Historicists as "resenters", or more specifically as one of the "six branches of the School of Resentment: Feminists, Marxists, Lacanians, New Historicists, Deconstructionists, Semioticians."
I found this via the article "The Neglect of the Author in New Historicism" by Patricia Ana Marquez, which says:
In his introduction to The Western Canon (1994), Harold Bloom writes a controversial polemic against New Historicists. His work attempts to map the influence of writers belonging to the Western “canon,” showing that every great writer has been influenced by a writer preceding him or her. The “canon” is in jeopardy according to Bloom, and he writes that he finds it “absurd and regrettable” that an author like Shakespeare is critiqued through a New Historical lens, reducing him to the “‘social energies’ of the English Renaissance” (3). Bloom perceives this reduction with disdain because Shakespeare, arguably the most influential writer in the English language, has been aesthetically lumped into comparability with less significant writers. One of the reasons, according to Bloom, is due to a trend in schools to discard aesthetics. In trying to “expand the canon” by including all forms of literature previously neglected in history, scholars have instead destroyed the canon (7).
His description of New Historicism in the above-quoted paragraph may be paraphrased as reducing literature to a footnote of history - "Shakespeare is only a signifier for the social energies of the English Renaissance" - but the exact phrase "footnote of history" does not appear. Searching through the full text of some of his books such as The Western Canon and The Anxiety of Influence does not give any results for this exact phrase, nor does it appear in a Google Books search in any of his books. I couldn't track down any original source for this phrase in reference to New Historicism; it may have been coined by whoever wrote that Wikipedia page, since everywhere I can find on the internet that mentions both "New Historicism" and "footnote of history" looks as though it's sourced or copied from that same Wikipedia page.