Firefox not visible because of a phantom display

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Level 4

1,357 points

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 Evidently Firefox remembers which display was last used and will use it next time, even though the display is is no longer active.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 4:00 PM

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Answer 1

C F McBlob

Level 4

2,885 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.

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Answer 2

Drew Reece

Level 6

10,660 points

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 Evidently Firefox remembers which display was last used and will use it next time, even though the display is is no longer active.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

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Answer 3

Michael Paine Author

Level 4

1,357 points

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...

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Answer 4

Michael Paine Author

Level 4

1,357 points

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.

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