I'm encountering the problem with TB, not FF.
I removed a bunch of "print_to_filename" preferences from prefs.js and that made the problem go away.
When I printed to a file after removing those preferences and then exited from TB, new "print_to_filename" preferences were not saved in prefs.js.
This suggests to me that these "print_to_filename" resources are obsolete. If so, then shouldn't part of this fix involve removing them, at least during a transition period? Otherwise, every user encountering this problem is going to have to use the advanced configuration editor or a text editor to remove them manually from prefs.js, which doesn't sound to me like something we want to be telling end users they need to do.
I'm encountering the problem with TB, not FF.
I removed a bunch of "print_to_filename" preferences from prefs.js and that made the problem go away.
When I printed to a file after removing those preferences and then exited from TB, new "print_to_filename" preferences were not saved in prefs.js.
This suggests to me that these "print_to_filename" resources are obsolete. If so, then shouldn't part of this fix involve removing them, at least during a transition period? Otherwise, every user encountering this problem is going to have to use the advanced configuration editor or a text editor to remove them manually from prefs.js, which doesn't sound to me like something we want to be telling end users they need to do.