Off and on I've been irritated that Firefox print-to-file functionality defaults to postscript with the filename before the .ps extension blank. What's up with that? This is more of an issue now that I have a Kindle, and thus print to PDF much more often than to paper, so tonight I poked through about:config, shrugged, and turned to Google. I found one useful page, http://ubuntuforums.org/showpost.php?p=7890849&postcount=7, but prefer "my" way to his, simply because my filter places exactly the right configuration lines on the screen, leaving nothing to manual hunting.
1) Enter about:config.
2) Type print_to_filename in the filter bar.
3) Place exactly the same path, file name, and extension in each setting.
This is what mine now looks like:
Needless (I hope) to say, different folks will have different printers, and so my entry for an HL-2040 will be atypical and most other people will have printers not shown here.
There is no generally-useful file name, so indicating the application that generated the PDF seems a reasonable choice. IMHO, /tmp is the only reasonable directory to use so that the user's home directory isn't littered. Littering $HOME is an unfortunate tendency of Linux developers.