This looks like the scam reported here: https://bugzilla.mozilla.org/show_bug.cgi?id=1668322

Either that website is malicious, or it is the website that's been hacked.

Sites trigger printing by calling a script function called

window.print()

To prevent all sites from using that function:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box in the page, type or paste print and pause while the list is filtered

(3) Double-click the dom.enable_window_print preference to switch the value from true to false

If you are in a window where you can't easily access the menu, you can call up the print dialog using Ctrl+P.

There may be some sites where you cannot print as intended without letting them use window.print() so this change may cause problems on those sites.

Our telemetry shows that around 85% of prints are initiated by window.print() (presumably mainly via "Print" buttons on webpages). So setting dom.enable_window_print to false probably isn't a good idea for most people.