85
Demystifying StartupWMClass
(thoughts.greyh.at)
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
this post was submitted on 24 Jun 2026
85 points (98.9% liked)
Linux
66018 readers
357 users here now
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Rules
- Posts must be relevant to operating systems running the Linux kernel. GNU/Linux or otherwise.
- No misinformation
- No NSFW content
- No hate speech, bigotry, etc
Related Communities
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
founded 7 years ago
MODERATORS
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?
The desktop files are named
firefox.desktopandfirefox-nightly.desktop, both in/usr/share/applications.EDIT: For completeness, I also checked the window classes of the regular firefox:
It can be observed that it uses only the window class
firefox, but twice?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.
Hmm, but I thought the
StartupWMClassesin the desktop files are correct? I thought the issue is that firefox-nightly uses thefirefoxclass in addition to thefirefox-nightlyclassStartupWMClass is NOT needed if the .desktop file is named correctly.
I see, so I could remove it, but wouldn't I still see the same behavior, since firefox nightly apparently also uses the
firefoxwindow class?