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
      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