Following is from Buster, but it's the same on Bullseye:
# /usr/local/smnxt/seamonkey -P smnxt &
(seamonkey:1347): Gtk-ERROR **: 15:41:01.711: GTK+ 2.x symbols detected. Using GTK+ 2.x
and GTK+ 3 in the same process is not supported
ExceptionHandler::GenerateDump cloned child 1353
ExceptionHandler::SendContinueSignalToChild sent continue signal to child
ExceptionHandler::WaitForContinueSignal waiting for continue signal...
(crashreporter:1358): Gtk-ERROR **: 15:41:01.774: GTK+ 2.x symbols detected. Using GTK+
2.x and GTK+ 3 in the same process is not supported
[1]+ Trace/breakpoint trap /usr/local/smnxt/seamonkey -P smnxtmoz
# dd /usr/local/smnxt/seamonkey
/opt/trinity/lib/kgtk/libkgtk2.so (0x00007f477ddfa000)
# cat .xsession-errors
Xsession: X session started for root at Sun 13 Jun 2021 05:10:39 PM EDT
dbus-update-activation-environment: setting
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/0/bus
dbus-update-activation-environment: setting DISPLAY=:0
localuser:root being added to access control list
[tdebuildsycoca] tdebuildsycoca running...
XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
after 275 requests (275 known processed) with 0 events remaining.
[2021/06/13 17:19:28.132] kded: Fatal IO error: client killed
[2021/06/13 17:19:28.132] [tdeinit] Fatal IO error: client killed
[tdelauncher] Exiting on signal 15
XIO: fatal IO error 2 (No such file or directory) on X server ":0"
after 185 requests (185 known processed) with 0 events remaining.
No such problem running IceWM instead of TDE.
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based on faith, not based on science.
Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!
Felix Miata