The Firefox jpm extension ctypes-test-ext attempts to open the dll operations.dll. It then tries to call the c function do_operation().
do_operation() simply calls the function do_supporting() defined in supporting.dll. do_supporting() prints: "DOING SUPPORTING". Then do_operation() prints: "DOING OPERATION"
test.exe calls do_operation() to verify that DOING SUPPORTING and DOING OPERATION are printed to std out.
ctypes.open() within the Firefox extension fails to load operations.dll with the error code 126. However, if operations.dll does not depend on supporting.dll then Firefox can successfully open the dll and call do_operation().