The problem with this is that Popper wanted the criterion to function normatively. So for example, he argued that Marxism and Darwin's evolutionary theory were

The problem with this is that Popper wanted the criterion to function normatively. So for example, he argued that Marxism and Darwin's evolutionary theory were not falsifiable and hence not scientific. Since at least the latter was a well accepted scientific theory, it's clear that Popper didn't put forward falsificationism as an empirical generalization about which scientific theories are well accepted. (Popper later changed his mind about evolution.)