Clicking Buttons like "Done" and "Singleplayer" doesn't work and you have to do it twice.

Cannot confirm.

Your Java version is out of date. Please update your Java to the latest version: http://www.java.com/en/download/. Keep in mind that when using a 32-bit browser on a 64-bit OS the automatic version detection will only show the 32-bit version of Java, the 64-bit version needs to be downloaded manually: http://www.java.com/en/download/manual.jsp.

Please report if the issue persists with the latest Java version.

Please force a crash by pressing F3 + C for 10 seconds while ingame and attach the crash report here.

Kumassa, when I hold Alt and C nothing happens, on my keyboard there is a key called "FN"

F3 & C , not Alt & C