Comment 46 for bug 428588

I cannot enable duplex when printing from within firefox (7.01). The combo-box in the Page Setup tab of the print dialog simply shows just one option "One Sided". In KDE applications, it correctly shows all three options (one sided, long edge, short edge) but both firefox and chromium (non-KDE) do not. Selecting the autoduplex page sizes will not print two sided. With hpijs driver, it does show the long and short edge options in all tested applications, BUT it only prints an error message "Unable to open the initial device, quitting."
I did check the "duplexer installed" option in CUPS administration. I am on Oneiric Ocelot. I tried hplip 3.11.7 (repositories) and a manually downloaded 3.11.10. "hp-check -t" says "No errors or warnings.".