Because printing does not reliably work on OS/2 trunk builds yet, there is the adapted Stuart Parmenter's PrintPDF extension:
http://blog.pavlov.net/2007/11/07/firefox-extensions-oh-my/
https://addons.mozilla.org/en-US/firefox/addon/5971
After installing, it will display an extra menu item in the Firefox File menu that allows to print to a PDF file.
-> URL: http://weilbacher.org/Mozilla/printpdf-0.75-fx-os2.xpi