User Agent: Mozilla/5.0 (X11; Linux i686; rv:66.0) Gecko/20100101 Firefox/66.0

Steps to reproduce:

Press Ctrl+P to open the print dialog.
On the second TAB (maybe "page settings") choose "long-edge binding"
Press "Print" to print the page.

Actual results:

The output is always sigle sided.
When I search for duplex in about:config I can see an entry like:

print.print_duplex ... integer 1

It is even not possible to print from Thunderbird in duplex mode.
Additional info: When I check the properties of the print job on the printers display, I see always "paper size: letter, single sided". This should be "paper size: A4, double sided".

I can print duplex from all KDE (QT) apps and from Libreoffice.

The version of Firefox I use is: 66.0.5 from Mozilla on Fedora 30 or Windows 10

Expected results:

Firefox, Thunderbird should print duplex when it is set.

The priority flag is not set for this bug.
:dholbert, could you have a look please?

For more information, please visit auto_nag documentation.

Can someone please respond to this?