The fundamental idea of importance in Popperian epistemology is the reconception of rationality which rejects justification as the hallmark of reason and replaced it with the idea of critical evaluation. This is known as CriticalRationalism, based on the RejectionOfJustification.
NB : Phil is a Popperian (though his friends try to talk him out of it.)
Remember you can try too : AnyoneCanEditIt
Another quick way of understanding the difference between Popperianism and justificationism is that under justificationism beliefs are considered guilty (irrational) until proven innocent. Wheras in Popper, beliefs are considered innocent (rational) until proven guilty.
Contrast heuristics of authority : http://lib.nmsu.edu/instruction/evalcrit.html