In Firefox the "default printer" is the last printer that was used. There is no "application command" that I have ever heard of which controls the selected printer from any sort of "command line switch". But, there is a hidden preference in the "Configuration Editor" - '''print.save_print_settings''' which set to '''''true''''' which controls whether the "last used" is the default or not. https://support.mozilla.org/en-US/kb/about-config-editor-firefox You can a "toggle" that pref to false and see how that works for you.