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Demystifying StartupWMClass
(thoughts.greyh.at)
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this post was submitted on 24 Jun 2026
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I use Firefox nightly and recently switched to Wayland (KDE). Ever since I switched, the taskbar often displays Firefox nightly with the regular Firefox icon, and the name Firefox instead of Firefox nightly. After reading your blog post I'm thinking that the culprit could be an incorrect StartupWMClass. But I don't get why this issue never showed on X11 then.
Yeah something isn't being matched right. Might want to look at both .desktop files and compare them. Probably be pretty obvious when you look. =)
I just checked the
.desktopfile for firefox nightly. It contains onlyfirefox-nightlyas itsStartupWMClass. So I went ahead and also checked the window class firefox nightly is running as and found the following:Does this mean that firefox nightly is using both, the
firefoxand thefirefox-nightlywindow classes?Yep it has both applied. What are the actual .desktop file names?