PDF email attachment problem


Using a Linux Debian desktop.

Used to be able to open PDF email attachments in Opera and Firefox-esr browsers without downloading them.

Suddenly no longer able to open this type of attachment in Opera or Firefox-esr without downloading the attachments.

Also not able to open PDF files from various websites.

No changes at all have been made to the Debian system or any software on that system.

How can this problem be solved, please ?

It is not an option to download attachments on a regular basis.