I'm running the latest stable version of snap packaged Firefox (78.0.2) on Ubuntu 20.04.
I'm unable to print to my Brother DCP-L2500D Laser printer - I can see and select the printer, but when I attempt to print a document I get a "Printing Failed" dialogue.
I assume this is related to permissions and how snap packages are isolated from the rest of the system.
I can print successfully from Chrome browser which is installed via apt.