The quote came from Conjectures and Refutations, pg 309. I agree that it doesn't say what falenas108 claims. Plus a bit has been missed out at the end: " -- though only tentatively." Also, on the following page, Popper says:

For us [fallibilists] ... science has nothing to do with the quest for certainty or probability or reliability. We are not interested in establishing scientific theories as secure, or certain, or probable. Conscious of our own fallibility we are only interested in criticizing them and testing them, hoping to find out where we are mistaken; of learning from our mistakes; and , if we are lucky, of proceeding to better theories.

So Popper would not assert that theories can be established as definitely false.