Bug 507322

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SUMMARY

I am running firefox with mutliple profiles and therefore I created .desktop entries for all profiles.
This way, Plasma on X11 nicely groups all windows of the same profile together.

When I recently tried switching to Wayland on my Ubuntu 25.04, this behavior got completely broken.
Now all Firefox windows get grouped together in one big group, and also the symbol is not the Firefox symbol any more, but rather some yellow "W" placeholder icon.

STEPS TO REPRODUCE
1. Create a new Firefox profile called "private
2. Put the following in `.local/share/applications/firefox-private.desktop`:
```
[Desktop Entry]
Comment=
Exec=firefox --private -P private --class=firefox-private %u
Icon=firefox
MimeType=text/html;text/xml;application/xhtml+xml;application/vnd.mozilla.xul+xml;text/mml;x-scheme-handler/http;x-scheme-handler/https;
Name=Firefox private
NoDisplay=false
Path=
StartupNotify=true
StartupWMClass=firefox-private
Terminal=false
TerminalOptions=
Type=Application
Version=1.0
X-KDE-SubstituteUID=false
X-KDE-Username=
```
3. Open the "Firefox private" application from the start menu on Wayland

OBSERVED RESULT
- Firefox starts loading with the correct Firefox icon, but once the browser window has appeared, it has a yellow "W" placeholder application icon.
- Firefox windows of any profiles get grouped together in one big group in the task bar

EXPECTED RESULT
- Firefox windows all have the correct icon
- Each Firefox profile gets its own window group in the task bar 

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: plasma-workspace 4:6.3.4-0ubuntu2
KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.12.0
Qt Version: 6.8.3

ADDITIONAL INFORMATION