How to change default "Print to file..." settings

Fedora 27 + KDE + Firefox 58.0 Quantum + Thunderbird 52.5.2 here. In 2018.

When I "Print to File" from Firefox or Thunderbird, the dialog shown use a default file with a default location.

There is no option to set the directory separately or configure a default. Annoying. Less than stellar after 14 years of development, but, ok. (Hey, can I set in the KDE System Settings? Nah.)

Thunderbird

Firefox

A Google Search yields ridiculous responses from various fogeys.

Workaround: Edit the default in "about:config".

See also Editing configuration.

Firefox

In Firefox, go to URL "about:config" and look for "print.print_to". Edit as needed. This is less than stellar, but it is something.

Thunderbird

In Thunderbird, there is no URL bar, so go to "Menu: (Edit > Preferences) > Tab: (Advanced) > Button: (Config Editor). At least on Linux, this differs between systems: Menu differences in Windows, Linux, and Mac.