Since the landing of bug 656826 printing preferences are stored as printer_<printername>.print_* rather than print.printer_<printername>.print_* Also as print_printer rather than print.print_printer The old code used to store to a prefBranch the new code doesn't. This needs to be corrected to use the print. branch.

So as noted in bug 885759 comment 2, we used to add two copies of the "print." prefix. Bug 203937 removed one of those (intentionally, to fix the double-up). Then bug 656826 removed the other copy, via the pref API change. We should probably just revert bug 203937. (the one that removed the at-the-time redundant "print." prefix)

This adds back the line that was removed in bug 203937, as I suggested in my previous comment. (though with the updated string API, AssignLiteral). I changed a few contextual Append() calls with literal strings to AppendLiteral, too. I verified locally that this fixes the issue, with my STR in bug 885759. (basically, tweaking the print header string in the print options UI, and then inspecting about:config to see where the updated string is stored). Before this patch, a custom print header-left string will be stored in the pref "print_headerleft". After this patch, it gets stored in "print.print_headerleft", as intended.