Okay, then. A "popular front" is a broad coalition of persons (usually left and center-left) who oppose the powers-that-be. In this case, I side with all those who oppose the earthly powers-that-be who are in power solely because they have convinced the masses an invisible immaterial magic mind demands their homage.
An "agnostic" is, in my book, one who disclaims knowledge of the supernatural in general and revealed knowledge in particular. For more details on the nature of philosophical agnosticism, I recommend Leslie Stephen:
Meta-empiricism, of course, is a realm in which religious "gnostics" claim to obtain knowledge from beyond the material world which is observable to us all. This is the realm from which priests and their defenders (e.g. Plantinga) claim to be directly apprehending supernature.
The Agnostic is one who asserts what no one denies that there are limits to the sphere of human intelligence. He asserts, further, what many theologians have expressly maintained, that those limits are such as to exclude ... ' metempirical ' knowledge. But he goes further, and asserts, in opposition to theologians, that theology lies within this forbidden sphere.
An agnostic popular front, then, is a collection of persons who jointly oppose priestcraft, that is, the practice of deluding people into thinking special knowledge of the divine is given to a select few, who neither produce nor exchange nor manage anything of value, but survive solely by the largess of those who are bilked into sacrificing their own temporal well-being for the sake of a coupon which can only be redeemed (if at all) after their own funeral. Such a blatant scam makes even life-insurance seem like a good bet.
One need not be an atheist (or even a freethinker) to oppose priestcraftly gnosticism, one need merely stand against those who claim themselves especially entitled to heavenly revelation or earthly tithes.