How to set default "Page Setup →Page Size" as A4 in Firefox?

Solution 1:

I had this same issue today and found this post after searching Google. I fixed it in basically the same way as Android Eve laid out, just using the print.print_paper_name setting instead and using iso_a4 as the value.

So the long version, that's:

1. In the address bar, type about:config.
2. Enter print.print_paper_name in the filter box and press Enter.
3. Double-click the entry named print.print_paper_name.
4. Enter iso_a4 in the dialog box and press OK.
5. Notice that it now works fine, and upvote this response ;)

Solution 2:

Check out this man page:

paperconfig - configure the system default paper size

Synopsis

paperconfig [ -v,--version ] [ -h,--help ] [ -p, --paper papername | --force ]

Description

paperconfig sets the system (or default) paper to be used by tools using the papersize >file. It can either ask interactively for the paper to use or be called non-interactively >by scripts.

When the paper size has been changed, paperconfig notifies other packages of the change >by running the scripts in the /etc/libpaper.d directory.

Options

-v,--version
Print the version of paperconfig and exit.
-h,--help
Print help about usage and exit.
-p, --paper papername
Use papername if possible. If papername is not a valid paper, print an error message and exit.
--force
Force interactive selection of the system paper even if the actual paper is a valid one.

Environment

PAPERCONF Full path to a file containing the paper size to use; this file will be rewritten with the system paper size.

Files

/etc/papersize
Contains the name of the system-wide default paper size to be used if the PAPERSIZE variable is not set.

/etc/libpaper.d
Directory of scripts to run after the paper size has been changed. This package puts no scripts here, but other packages may.

So you would run paperconfig -p a4 in the commandline.