How do I get the Modern UI of Firefox in Windows 8?

Mozilla mentions

Elm is the experimental repository where most of our Metro development work has been happening.

Now, I grabbed the latest nightly from the Elm repo, installed it & then despite starting it from the start screen, I was still provided the desktop version.

Is there a way I can get the Metro Modern UI of Firefox in Windows 8? Do I need to add some extra command line arguments or something?

Answer

Ok, firstly, there seems to be a quirk in Windows 8: only the default browser can be launched with Modern UI. I have tested with IE, FF and Chrome on the Enterprise Evaluation and they will all launch the Desktop version unless set as default. Additionally, as soon as a browser is set as the default handler for HTTP/HTTPS, any other running Modern UI is instantly closed. More information is available at this question.

So, I have it running fine. There were a few things I did, any of which may be responsible:

• 
  

  Installed an older Firefox build (FF 18), specifically the installer executable

  
  


• 
  

  Set as default for all via Control Panel => Programs => Default Programs => Set Default Programs => Nightly

  
  

  
  ^{Click for full size}

  
  


• 
  

  When the Modern UI version launched, but hung with a blank screen, I closed it via Task Manager, set IE back to default, and set Nightly to default again. At this point, the Modern UI version of FF worked.

  
  


• 
  

  Installed the latest elm build (FF 19, 24-Oct-2012 06:06), again from the installer executable. Restarted.

  
  

So, now I have Nightly running with Modern UI:

^{Click for full size}

^{Click for full size}