Yes, only causality is observable, in fact, all of our science depends on it. Sure, some freaky stuff happens at the sub atomic level, but there is literally no evidence(and plenty to the contrary, some available in this very thread) that any of that sub atomic freaky stuff negates causality. In fact, many speculate 'causality' could not operate sans 'sub atomic freaky stuff'.
The idea of human freewill is simply religion.
By the way, 'falsifiable' means that there is a conceivable finding that could disprove a theory. All scientific findings must be 'falsifiable' else they cease to be science.