That would be something in your Printer software driver setting to do that.

This is a Firefox setting, not my printer settings. I can print non sequential pages in duplex in all other web browsers. It is not an option in Firefox.

So if you check on printer properties does it show the duplex option in there? And have you check the manufacture site on print issues?

I have not checked the printer properties because I have been able to print duplex non-sequential pages on other browsers and all the apps that I use, i.e. MS Excel for many years using this printer. This issue only is present when I try to print from Firefox.