According to Popper, a theory is scientific if and only if it is falsifiable in the sense that there is some prediction of the theory, which can be tested or compared with reality and thus be falsified if it comes out negative. According to Popper a scientific theory can never be verified, only be made more or less credible or scientific by passing more or less severe falsifiability tests.
A scientific theory is based on certain basic assumptions and it is natural to ask about falsifiability of the basic assumptions, and not only about falsifiability of consequences of the basic assumptions as predictions of the theory. One may argue that falsifiability of the basic assumptions of a theory would be an advantage from scientific point of view.
However, modern physics is based on assumptions which cannot be tested against reality and thus cannot be directly falsified, only indirectly via consequences.
The basic assumption of molecular chaos of statistical mechanics, cannot be directly tested against reality. Neither can basic assumptions of quantum mechanics such as the assumption that the wave function is either symmetric (bosons) or anti-symmetric (fermions), be tested against reality, because the wave function for a multi-electron system cannot be captured (experimentally or theoretically) and studied. Not to speak of string theory, where even the basic assumptions are unknown.
But the final objective of Popper’s falsifiability test is to test the validity of the theory including its basic assumptions. Popper then says that the more falsifiability tests a theory passes, the better is it validated.
But verifying assumptions by observing consequences of the assumptions, is possibly one of Aristotle’s logical fallacies: If you spit on a stone it becomes wet, but if you observe a wet stone you cannot conclude that it is an effect of spitting.
It is natural to ask why Popper did not ask for falsifiability of the basic assumptions, only for possibly very farfetched consequences? Isn’t the validity or truth of the basic assumptions the most essential aspect of a theory? Was Popper adjusting his test to modern physics, where the basic assumptions are not directly falsifiable?