cairo_win32_print_gdi_error() use fwprintf with a char* format.
It should also flush stderr so that all error messages appears before exit.
The above two problems results in no GDI errors being printed in Firefox.
Fixed in mozilla-central for Firefox 4:
Author: Mats Palmgren <email@example.com>
Date: Fri Jan 21 09:52:19 2011 +0100
win32: Improve error logging
On win32 stderr is fully buffered, so fflush() should be called after
each error to ensure it is printed to the console.
There is no need to use fwprintf if the format string can be
represented as char*.