It turns out that mozilla, as per the gtk2xt code selects for input on
the socket with a mask of 0x0fffff (for god knows why) which includes
ButtonPressMask, causing a BadAccess if someone else also selects for
this. As per the client-side windows merge we always normally selects
for button press so we can emulate it on client side children that
selects for button press. However, we don't need this for GtkSocket,
so we unselect it here, fixing the crashes in firefox.