1434523 - Firefox scaling on 4k display doesn't recover after loading another application in Full Screen mode.

Status: RESOLVED DUPLICATE of bug 1426874

(Firefox :: Untriaged, defect)

Description

[nimbice]

Attachment: SS.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20180128191252

Steps to reproduce:

Started Firefox and used it normally.  Eventually loaded a video game in full screen mode.  Not full screen windowed, actual full screen.  Once I was done playing and exited the game my computer returned to my desktop.  I've done this with several games and always the same result.  Fullscreen Windowed mode does not cause this issue.


Actual results:

Upon exiting the game, Firefox was scaled back to 100% instead of the 250% I had the computer set to before starting the full screen game.  As such all of the elements of the window were extremely tiny.  Once Firefox is closed and re-opened it returns to normal scaling.  While writing this report I opened Deadspace 3 into Fullscreen mode and alt-tabbed out and the issue recurred.  I've attached a screenshot showing a run box for scale.  You will notice the title bar on the run box is far larger than Firefox.  The run box is normal size and this text is too small to read on my screen.  Forgive any typos, I cannot see what I'm writing.  :)


Expected results:

Firefox should have returned to normal scaling after exiting the full screen game session without having to restart.

Comment 1

[Cristina Badescu [:cbadescu], Experiments QA]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20180128191252

Hello,

I cannot test this using the steps to reproduce because I don't have any similar game on my testing machine.

However, I've changed the browser's zoom level page, on latest Firefox release 58.0.1 and  manually changed the display resolution,  but I didn't encounter this issue: the changed zoom level wasn't affected.

Can you be more specific on how did you change your browser scale? Did you change the value of the "layout.css.devPixelsPerPx" pref from the "about:config" page? Or did you just change the zoom level of opened pages?

Did you encounter this issue on other Firefox versions, such as 57 or even older?

Also, can you please retest this using a new clean Firefox profile (https://goo.gl/AWo6h8), maybe even safe mode (https://goo.gl/AR5o9d), to eliminate custom settings as a possible cause?

Comment 2

[nimbice]

To produce this issue I would open a full screen application, common to video games though not unique.  Most games have a full screen mode available. However, today I'm unable to reproduce the issue entirely.  I believe the only change I made was a reboot, perhaps something was incomplete with a recent Windows Update or video driver update etc?  I'm uncertain to the particulars but as of this evening I can no longer reproduce the issue which was previously reproducible 100% of the time.

To clarify how I used to produce it, I would open a full screen application such as a game, and then either alt-tab out or close the game.  Both elicited the same response from Firefox prompting me to suspect the scale change in Firefox was taking place at the time of my computer entering full-screen mode rather than upon exit or switch.  I would not make any settings adjustments to Firefox prior to this issue occurring.  All Windows applications (that are compatible) apply the Windows Desktop Scaling settings when they load (unless compatibility settings have been configured to override it of course).  Firefox was not retaining the desktop scaling setting after using a full screen application until Firefox was closed and reopened.  After using a full-screen application Firefox appeared to revert back to a desktop scaling level of 100%, which is the setting that indicates no scaling is being applied at all.  All other programs would remain at 250%, which is what I had my desktop scaling set to, only Firefox seemed to revert and only after opening a full screen application.  Since I keep my desktop at 4096x2160 this made Firefox quite tiny relative to other open programs, as shown in the screenshot.

I do not know that I encountered this issue on previous versions of Firefox as I'm quite unaware whether I have used any previous version.  I've never looked at my Firefox version number before filing this bug report.  I know Firefox has upgraded itself a few times since I started using it but I've not used it for very long.  I only first noticed this issue in the last week but I normally don't run any applications in Full-Screen mode as I prefer Fullscreen-Windowed which isn't a true "full screen" in the classic sense of the mode.  I happened to be playing a game that did not support the Full-Screen Windowed option and saw this bug recur a number of times over the course of a few days.

While it remains odd that Firefox was the only program to respond this way I would have to attribute this particular bug to a temporary state on my own PC more so than a fault with Firefox itself on account of it being allegedly resolved with a reboot.  Please feel free to close this entry.  If you are troubleshooting other similar issues and would like to query me for any further information please feel free, I'll oblige as best I can.  Thank you very much for you attention, and I apologize if I have wasted your time.

Thanks,
Alan

Comment 3

[Cristina Badescu [:cbadescu], Experiments QA]

Hello Alan,

Thanks for the detailed explanation. 
It seems that this behavior that you're encountering sounds very familiar with the one described in bug 1426874.
I'm going to mark this issue as Resolved-Duplicate of the mentioned bug.

Comment 4

[nimbice]

I agree they do seem quite similar.  I've not managed to reproduce the issue since on my end so I doubt I'll be able to contribute anything helpful.  Best of luck, hope you're able to pin it down!

-Alan