Hmm, I wonder what changed.

The pdf.js demo at https://mozilla.github.io/pdf.js/web/viewer.html seems to still be working, although it could be a different version from the one you're running. Looks like the latest release was May 30th: https://github.com/mozilla/pdf.js/releases

Any chance this is a Tracking Protection issue? The shield icon toward the left end of the address bar usually turns a bit purplish when content is blocked. Click the icon to learn more or make an exception. See: Enhanced Tracking Protection in Firefox for desktop.

There wasn't a Tracking Protection issue for this. I checked and this was created with version 1.5.343.

Hmm, maybe that release was from around 2016?

Does it make any difference if you test the page in Firefox's Troubleshoot Mode (formerly known as Safe Mode)? In that mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is running:

You can restart Firefox in Safe/Troubleshoot Mode using either:

• "3-bar" menu button > Help > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)
• (menu bar) Help menu > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)

and OK the restart. A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

If Firefox is not running:

Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.) A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

Note: Don't use the Refresh without first reviewing this article to understand what will be deleted: Refresh Firefox - reset add-ons and settings.

Any difference? If so, I would suspect the ongoing changes to graphics and rendering.

No difference in Troubleshoot mode.

Unless there is a public-facing website with this problem, it's going to be difficult for any of the support volunteers to figure out what is going on.

Ok. I copied all of this to one of our servers that has public access. You can access it at: http://www.gel-mobile.com/web/viewer.html?file=/web/raw.pdf

Thanks for looking at this!

Strange. Firefox is extracting the text and generating the searchable/selectable trasparent text layer, but the canvas which should show the image conversion of the document is just white.

I don't see any relevant-looking script errors in the web console.

Someone with extra time could run the Mozregression tool to pinpoint the patch that caused the canvas to become invisible. https://mozilla.github.io/mozregression/

However, since it is an older version of the viewer, I don't know whether it would be a priority fix, unless other sites also are affected.