Eventually, every Linux user opens an app and finds a generic placeholder icon staring back from their dock/panel. It looks like the dock is broken, but it almost never is - the cause is a single line in the app’s .desktop file, and it only takes a minute to fix. Here’s how to find it and fix it yourself, on any desktop.

As the maintainer of Plank Reloaded, the most common bug report I get is “this app has the wrong icon.” It’s almost never the dock - it’s a broken StartupWMClass in the app’s .desktop file. So I wrote up how to find the right value on X11, Wayland, and KDE, and why deleting the line often fixes it.

  • angel@sopuli.xyz
    5·
    21 hours ago

    I just checked the .desktop file for firefox nightly. It contains only firefox-nightly as its StartupWMClass. So I went ahead and also checked the window class firefox nightly is running as and found the following: Screenshot showing the window properties of firefox nightly in the KDE system settings

    Does this mean that firefox nightly is using both, the firefox and the firefox-nightly window classes?

      • angel@sopuli.xyz
        1·
        6 hours ago

        The desktop files are named firefox.desktop and firefox-nightly.desktop, both in /usr/share/applications.

        EDIT: For completeness, I also checked the window classes of the regular firefox: Screenshot of the KDE system settings displaying properties of the normal non-nightly firefox window

        It can be observed that it uses only the window class firefox, but twice?

        • zquestz@lemmy.worldOP
          1·
          6 hours ago

          Yeah in your case the best fix is probably REMOVING StartupWMClass from those launchers if it is present. Then it will only match the app id on the .desktop file name.

          • angel@sopuli.xyz
            1·
            6 hours ago

            Hmm, but I thought the StartupWMClasses in the desktop files are correct? I thought the issue is that firefox-nightly uses the firefox class in addition to the firefox-nightly class