Did you contact their Support line for help on their software? Printer driver or printer software issues isn't a firefox End User help.

Ignore the above reply as it is misleading information.

This forum is for support of things in relation to the desktop Firefox web browser.

The JS_print extension like many others on the site were Legacy extensions that worked on Firefox 56 and earlier (including the old EOL 52.9.0esr). Since they do not work Firefox 57 and later there was no point hosting the Legacy versions of the Extensions anymore on https://addons.mozilla.org/firefox/

Any Legacy Extensions the third-party authors or company made for SeaMonkey that also supported Firefox are listed in https://addons.thunderbird.net/seamonkey/