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I purchased a new MacBook Pro 15 (2017) and immediately installed Mojave. I then started to see red pixels appearing on the same line as the top menubar. It happens very rarely, but has already occurred about 4 times per week. Pixels disappear if you move any window. I noticed this while using Firefox and iTerm.

Could it be an issue with hardware (dead pixels) or software (Mojave dark theme) ?

example

  • 1
    Do you see them if you switch to the Light theme? – Jesse P. Oct 2 '18 at 12:11
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    I'd switch to Light mode for a week and see if it comes back even once. If not, you could extend your test window to see if it is just more random or consider the mystery solved as being a bug in the Dark theme (the choice would be yours). If it does happen with the Light theme, I'd say it's likely a bad pixel or bad hardware and would suggest a visit to the nearest Apple store for an RMA or repair. – Jesse P. Oct 2 '18 at 12:23
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    Same problem here, seeing this also in the dark mode. I noticed it when using the telegram app (MacBook Pro 13 2018) – Florian K Oct 2 '18 at 12:30
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    I've been noticing the same thing since upgrading, last 2018 MBP 15in. Mostly seen on Firefox, but also iTerm and Atom (I want to say it was grey on one of those). Seen it on both the top and bottom edge and it tends to blink. The cursor can cover over it, so I don't think it's the monitor. Have you noticed any other graphical glitches? – Alexander O'Mara Oct 5 '18 at 19:43
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    I updated to Mojave yesterday and have exactly the same issue (in Firefox, on the top edge of a tab bar). Seems to be a software glitch, related to graphics/GUI... especially when there is a movie playing. – maxx Oct 12 '18 at 20:27
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It's definitely not a dead-pixel issue. I've determined it's probably a software bug introduced in Mojave. I'm not able to screenshot the glitch in most cases (the glitch will typically immediately disappear), but I have managed to capture it on a couple of videos and screenshots.

The fact that it can be captured in software and the fact that the cursor can cover over the glitched pixels indicates the issue is not in the monitor but happening in software.

Examples:

Firefox

Here's a screenshot from a screen recording of Firefox, where you can see the grey pixels.

enter image description here

Interestingly, if we zoom in a bit, we can see the pixels are actually outside the window itself.

enter image description here

Finder

I've also captured similar glitches happening in Apple's own Finder on regular screenshots.

enter image description here

enter image description here

Notes:

Some interesting things to note about it.

  • I've only seen it happen against dark areas of a window.
  • It can happen in both light mode and dark mode (if the window is dark anyway).
  • It mostly happens at the edge of a window (where the shadow is), though I have seen it on the inside of some.
  • It often (but not always) disappears when window focus changes, among other things (window focus changing causes window shadows to change).
    • I've been able to change focus to and from an iTerm window with no shadow (when transparency is enabled), and the glitch outside the bottom edge of the window persisted.
  • It can be captured with QuickTime Player's Screen Recording feature.
  • Mysteriously, though it can be capture with QuickTime, it is invisible to Apple's developer tool Pixie, as seen in this screen recording. Likewise, the Digital Color Meter app does not see it either.
  • I've seen it mostly in grey and red, but also green, yellow, and more colors.
  • The glitch can happen even when Finder is not running, so it's not a part of Finder.
  • Running killall Dock while SSH'd into a machine displaying the glitch may cause it to stop, though this may just be a side-effect of shadow changes.
  • I tried suspending all the Firefox processes (firefox + plugin-container processes) over SSH with kill -SIGSTOP while the glitch was happening and the glitch continued to blink, further indicating the glitch is happening outside the Firefox processes.
  • Going further, I tried systematically suspending processes over SSH, to see which one might be responsible. The only one suspending causes the flashing to freeze with was WindowServer.
  • Using the Quartz Debug developer tool (one of the Xcode addition tools, mentioned here), I tested some of the options it had. When the "Disable 2D Acceleration" option was enabled, I was unable to reproduce the glitch like I could when it was disabled. The Autoflush drawing and Vertical Sync options had no effect.
  • It seems to only happen with the integrated graphics card. I have not been able to reproduce it while the discrete card is active.
  • So far I've only heard reports of it happening on recent MacBook Pro and MacBook Air models. I was unable to reproduce this issue on a previous generation MacBook Air running the same OS version.
  • I've not yet seen it happen in a Mojave VM using VMware Fusion, further indicating it only happens with certain hardware.
  • To remove all variables, I tried running a clean install of Mojave 10.14.1 on an external drive. With all default settings, I was quickly able to reproduce it Light Mode with Firefox 63.0.1 with the dark theme and dark developer tools theme enabled and the console open (screen recording).
  • Browser-like applications appear especially likely to trigger it (ie. Firefox and Electron-based apps).
  • Applications I've seen it with (I've probably forgotten some):
    • Firefox
      • Top edge (requires dark Firefox theme)
      • Bottom edge (requires dark bottom of window from open search bar with dark theme, dev tools with dark theme, or dark web page content). Also done on a clean 10.14.1 install.
    • Atom (may require Settings > Core > Title Bar > custom)
      • Top edge
      • Bottom edge
    • Discord
      • Bottom edge
      • Inside window
    • iTerm (with a black, semi-transparent background; it does not seem to happen with an opaque background)
      • Top edge
      • Bottom edge
      • Inside window (at the bottom edge of one pane with split panes)
    • Finder
    • Activity Monitor
      • Top edge
    • Disk Utility
      • Top edge
    • Console
      • Inside window (over the transparent column headers)
    • Mail
      • Inside window (over the transparent column headers)
    • Archive Utility
      • Top edge
    • Hex Fiend
      • Top edge
    • Google Chrome (when using macOS dark mode)
      • Inside window at chrome://downloads/ under light grey horizontal line of top menu bar)
  • I've also seen it happen once at the bottom edge of the drop-down menus from the top menu bar.
  • The selection of apps and places I've seen it with make me suspicious it may in some way be window transparency related.

Things that have no impact on the glitch (tested with Firefox):

  • Doing a clean install of 10.14.1.
  • Resetting PRAM.
  • Resetting SMC.
  • Open the app in low resolution mode.
  • System Preferences:
    • Display resolution scaling.
    • Display color profile.
    • Night Shift.
    • System accent color.
    • Auto-hiding dock.
    • Accessibility > Display > Use grayscale
    • Accessibility > Display > Invert colors

Hardware:

I've only heard claims of it affecting different MacBook Pro models from 2016-2018 and the 2018 MacBook Air (the models with USB Type-C). If you are seeing this issue on another Apple computer model, or don't have this issue on one of the affected models, I would be interested to hear about it.

Conclusion:

Unfortunately, I don't think there is any way to prevent this glitch at this point, aside from forcing the use of the discrete card if your computer has one (and you don't mind the reduced battery life), but hopefully it will be resolved in a future update.

Even more unfortunate, it still has not been fixed in any version from 10.14.0 through 10.14.6 or the second supplemental update since. I filed a bug report on bugreport.apple.com (not public, but 46079638), which has been marked as a duplicate of 45841204. I don't have access to that bug report, but thought I would mention it in case anyone wants to reference it.

Reportedly it is still present in 10.15 Catalina (MDN bug report).


Steps to reproduce:

I've had the best luck reproducing the bug with Firefox.

  • Open Firefox (63.0.1 in my case)
  • Set Firefox theme to Dark
    • View > Toolbars > Customize... > Themes > Dark
  • Navigate to a page like http://example.com/
  • Open developer tools
    • Tools > Web Developer > Inspector
  • Set developer tools theme to dark
    • In the top right, click ... > Settings > Themes > Dark
  • Click the Inspector tab
  • Open the console
    • In the top right, click ... > Show Split Console
  • Ensure the developer tools covers the bottom of the window
    • If it doesn't, in the top right, click ... > Dock to Bottom
  • Reload the page until the glitch happens

References:

Possibly loosely related: Avoid using a transparent surface by using CoreAnimation (if my suspicion that it is transparency related is correct, that change may eventually have an impact on this bug happening with Firefox, if only by avoiding the OS bug).

  • I have a Macbook Air 2018 running Mojave and this same issue appears (daily for me) between the top edge of Firefox and the bottom edge of the menu bar. – mttpgn Mar 29 at 11:11
  • @mttpgn Good to know it also impacts the new MacBook Air. – Alexander O'Mara Mar 29 at 16:14
  • Nice analytical work! On a side note, if you have Firefox installed, it's not a clean install, rather a newly setup system. A clean system has only the default apps, nothing which gets installed after the setup. Very important in some cases, as apps usually change parts of the system (like installing new fonts), which can cause all kinds of bugs to appear which have nothing to do with the OS. Still calling it clean install can lead to frustrations with support if you ever try to go through them... – Carl Dombrowski May 15 at 21:07
  • I joined this community to upvote your answer. I also see this happening multiple times a week. Running a 2018 MBA in dark mode on Mojave 10.14.6 , and FF 68.3.0 esr – Luuklag 37 mins ago
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Partial solution for me currently is to put the affected apps into fullscreen mode.

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This is very much a software issue. It’s reproducable on two different MacBook models running Mojave and two different LG USB-C type displays for me.

Don’t seek hardware repair or reinstall your os if this is your only symptom. Updating software when available is advised since this could be a bug that will get patched.

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