In recent years I’ve seen very well-known physicists try and make this argument: string theory is falsifiable, because if an experiment shows quantum mechanics fails, then string theory would be falsified.
It’s hard to know where to start with this, since it seems to me on its face absurd, and makes me worry about the people making it. One comment would be that even if an experiment were done falsifying QM (very unclear what that even means) then it is likely that some idea associated with string theory would get invoked as a possible explanation. Other than that, of course when one is talking about falsifying an idea, one means falsifying the distinctive aspects of the idea.
For an alternate version of this answer, see
http://www.math.columbia.edu/~woit/wordpress/?p=5358&cpage=1#comment-136521
