Karl Popper believed that scientific knowledge is provisional – the best we can do at the moment.

That directly contradicts your statements on certainty and was the whole point of the first half of my comment:

And what kind of proof would that have to be, for you to be certain that something is true ?

Certainty is neither required to have justified beliefs nor is it achievable. OP made no claims of "certainty"; they simply asserted their belief.

anything other than that simply falls under uncertainty, but could still be both possible and probable.

Everything is uncertain. But to varying degrees. If I believe that there's a 99% chance that X is false, then colloquially, I believe that X is false. Otherwise we'd never be able to use that sentence. I don't think many people equate the two either.

Any claim which positions itself as an absolute requires to be proven

Any claim which positions itself as an absolute cannot be proven to be an absolute. Any claim which positions itself as an absolute - dogmaticism - is deeply irrational.