Recently firefox has started printing everything in duplex (double sided). The print dialog that pops up when printing has the duplex box unchecked, so should print single sided. In about:config print.printer_HP_LaserJet_4050_Series_PCL_5.print_duplex is set to 2. If I change this to 0 I get single sided printing for a random small amount of time, but at some point it reverts to 2 and duplex printing. This does not occur in other browsers.