FREENX server and NX client - Unable to start firefox - OS 12.3

Hello
Connecting to the server from a linux notebook thru nxclient is OK.
But I am unable to start firefox.

After another try from command line, I got these errors :

LINUX-TEST-123:~ # firefox
###!!! ABORT: X_SendEvent: BadValue (integer parameter out of range for operation); 9 requests ago: file /home/abuild/rpmbuild/BUILD/mozilla/toolkit/xre/nsX11ErrorHandler.cpp, line 157
###!!! ABORT: X_SendEvent: BadValue (integer parameter out of range for operation); 9 requests ago: file /home/abuild/rpmbuild/BUILD/mozilla/toolkit/xre/nsX11ErrorHandler.cpp, line 157
LINUX-TEST-123:~ # The program 'crashreporter' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadValue (integer parameter out of range for operation)'.
  (Details: serial 132 error_code 2 request_code 25 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

LINUX-TEST-123:~ # 

The file

/home/abuild/rpmbuild/BUILD/mozilla/toolkit/xre/nsX11ErrorHandler.cpp

does not exists on my system

Any help is welcome.