Firefox 91 emits error "Unknown paper size"

Solution In Progress - Updated -


If a $HOME/.cups/lpoptions file exists, Firefox 91 shows the following error:

(firefox:16955): Gtk-WARNING **: 09:16:28.873: Unknown paper size

Also, Firefox uses A5 as paper size when printing, even if the printer is configured for A4, and each user must manually change the paper size before printing.


  • Red Hat Enterprise Linux (RHEL) 8.5
  • Firefox 91

Subscriber exclusive content

A Red Hat subscription provides unlimited access to our knowledgebase, tools, and much more.

Current Customers and Partners

Log in for full access

Log In

New to Red Hat?

Learn more about Red Hat subscriptions

Using a Red Hat product through a public cloud?

How to access this content