The flash plugin does not work with Xephyr when it's run over a 16 bit color
depth X server. The gecko based browsers firefox, galeon and epiphany exits with
the following error message (with a different serial):

The program 'Gecko' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
  (Details: serial 114 error_code 8 request_code 129 minor_code 3)
  (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.)

With konqueror, the following error message is outputed several times:
X Error: BadMatch (invalid parameter attributes) 8
  Major opcode:  129
  Minor opcode:  3
  Resource id:  0x2400008

I've tested both in Debian Sarge with Shockwave Flash 7.0 r25 and Ubuntu 5.04
with Shockwave Flash 7.0 r61.