Michael Paine

Q: Firefox not visible because of a phantom display

I have a 2010 iMac running 10.9.2

 

I have had a problem where Firefox started but nothing showed on the display. MIssion Control did not show that any extra displays were in use. Eventually I realised that a VGA adapter was plugged into the back of the iMac but was not connected to an active display. I unplugged the adapter and Firefox appeared on the main display.

 

It seems that Firefox was using this phantom display even though it was not recognised by Mission Control. The problem occurred after I moved Firefox to the VGA display and forgot to move it back to the main display. Evidently Firefox remembers which display was last used and will use it next time, even though the display is is no longer active. Other apps might have the same limitation.

Posted on Apr 30, 2014 4:02 PM

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Q: Firefox not visible because of a phantom display

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  • by C F McBlob,

    C F McBlob C F McBlob Apr 30, 2014 7:36 PM in response to Michael Paine
    Level 4 (2,865 points)
    Apr 30, 2014 7:36 PM in response to Michael Paine

    Leaving that adapter plugged in is what caused this, more likely than not. Whenever you do that, OS X can still indicate that a display is connected but not turned on, and Mission Control will still try to use a Space for it.

  • by Drew Reece,

    Drew Reece Drew Reece Apr 30, 2014 7:38 PM in response to Michael Paine
    Level 5 (7,552 points)
    Notebooks
    Apr 30, 2014 7:38 PM in response to Michael Paine

    Michael Paine wrote:

    It seems that Firefox was using this phantom display even though it was not recognised by Mission Control. The problem occurred after I moved Firefox to the VGA display and forgot to move it back to the main display. Evidently Firefox remembers which display was last used and will use it next time, even though the display is is no longer active. Other apps might have the same limitation.

    I think all apps will exibit this behavior the OS tries to keep windows on the same screen.

     

    You could also disable the 'Mirror' option, if you have it in System preferences (it's unclear to me since this is document for 10.8 & I don't have dual monitors).

     

    OS X: How to use multiple displays with your Mac in Mountain Lion and earlier

  • by Michael Paine,

    Michael Paine Michael Paine Apr 30, 2014 10:22 PM in response to Drew Reece
    Level 2 (348 points)
    Mac OS X
    Apr 30, 2014 10:22 PM in response to Drew Reece

    Thank you. I tried changing display settings, mirroring and the like. As I said, MIssion Control did not show the VGA adapter as a "space" but, it seems, Firefox thought it was still available.

     

    As it happens, I now use Air Parrot to "Airplay" my iMac display to an Apple TV. That is why I no longer connect to my projector with the VGA cable. The iMac is too old for Airplay to work directly with video and so needs Air Parrot - but that is another discussion...

  • by Michael Paine,

    Michael Paine Michael Paine Jul 11, 2014 3:41 PM in response to Michael Paine
    Level 2 (348 points)
    Mac OS X
    Jul 11, 2014 3:41 PM in response to Michael Paine

    Found a solution in some old Firefox discussions

     

    1. Unplug VGA adapter

    2. Start Firefox - it should open on the main (only) display

    3. Maximise the window (click on green dot in top left) or View/Full screen

    4. Reduce back to normal window

    5. Quit Firefox

    6. Plug in VGA adapter

    7. Start Firefox - it should open on the main display

     

    It seems the action of maximising then reducing the screen makes Firefox remember the display it was last using. I vaguely remember maximising one time when I was using it on the external display.