Why did Karl Popper criticize the Marxist’s theory, not the Austrian Schools of Economics?

…as answered on Quora, January 31, 2019:

Probably because Marxists have “a theory of history” and are what Popper called “historicists.” Austrian economists were not.

Indeed, Austrian economists were major opponents of historicism.

Also, Austrian economists were generally liberal, in that they supported decentralized power structures (Wieser being a strange exception). Menger, Böhm-Bawerk, Mises, and Hayek were all proponents, in their different ways, of the “open society,” which Popper saw as the civilizational-level analog to the scientific method. Marxists, on the other hand, scorned such views. Remember how Marx pilloried “bourgeois freedom”? Marx also engaged in a rigid theory of ideology that saw it as a mere expressiom of economic class. That is a world apart from Popperianism and Austrianism.

Now, you may be wondering: but Misesian praxeology, following Menger’s “exact science” method, is not exactly a falsifiable procedure!

True to some degree. And one could mention that Hayek was not a praxeologist, and Hayek was the Austrian School economist that Popper knew best, and from whom Popper learned much. But consult Popper’s views on Darwinism. Evolution by “descent with modification” as directed by “natural selection” has also been attacked for its a priori character. Popper’s defense of this method might give us clues to how he would have thought about the rather a priori nature of the Menger-Mises position of the exact science of the discipline of human action.