I am using PDFCreator 2.4.1 with Windows 7/Firefox 50.1.0.
On some html pages, the print works OK. On more complex pages (ie with graphics), the “preparing” window comes up, the CPU usage goes through the roof (60-80%), the Cancel button is greyed out, Firefox shows the “Not Responding” status, and clicking the red X causes Firefox to go away.
this is not a PDFCreator window, you’d get the same printing to any other printer as this is during the spooling part of the job, so a combniation of windows spooler and Firefox problems or just insufficient memory.