Read the statement by Michael Teeuw here.
White Screen after starting Magic Mirror
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 Are you working on your raspberry directly? You should be able to switch with alt + tab. As an alternative you could run node serveronly, open the browser on your own and go to http://localhost:8080
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 Yes i work on raspberry directly. Sadly i did mot found a way to test my work on my mac!? Ok thanks! alt + tab is working. But it still s**** a bit when i have to restart my raspberry after ever fault i did… 
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 Ctrl+q quits the mirror, ctrl+r reloads the page. 
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 No. Ctrl + q is not working… It works when the mirror is running but with my white screen it is now more possible to quit it with this command… 
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 i got it! When i change with alt + tab to the Terminal i can close the Terminal and that also Quits my mirror! Thanks! 
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 @Squirrel 
 Yes, I forgot to mention that. You can also press ctrl + c in console to kill the mirror process. So you don’t have to close the terminal every time


