Thank you so much, for taking your time explaining me, what the problem is. As soon as I saw you jump height (which is about the half of the intentional one), I realized, that the problem is not what I expected it to be. I did not multiply gravity by delta. (Not using rigid bodies, this can happen...)
If you are still interested, it should be fixed by now. :)
Again thank you a lot! Without you I would not have realized this!
(On that note, different endings still don't work in the HTML version.)