Firefox Has Fixed Their PDF Viewer

[Gerowen]

I have, for a while now, had a unique problem with Firefox's PDF viewer.  One of my hobbies is a family tree that I work on with Gramps and occasionally render a massive PDF document to a virtual sheet of paper that's something like 40x40 inches.  When viewing this document you "have" to be able to zoom in between 300% and 500% to read everything.  This works fine in Chromium based browsers, but I noticed that with Firefox it almost seems like it renders the document once but then never scales or re-renders it again as you zoom in or out, which leads to even text getting blurred to the point of being illegible.  Here's a screenshot of what I see with Firefox ESR 128.  The images of folks that aren't me have been pixellated on purpose for their privacy.  The one in the middle is me and has not been modified in any way; this is just how it has always looked in Firefox for me.

However I recently added the mozilla apt repo to my Debian laptop and upgraded to Firefox 140 ESR and when viewing the same exact file in that version, it looks fine.  Here's a screenshot of what that same file looks like in the latest versions of Firefox.

I first looked into this because I ran a scan on the EFF's "Cover Your Tracks" scan and I saw that it detected the "Chrome PDF Viewer", so I thought maybe they had switched from their existing PDFJS engine.  However, when reverting back to Firefox 128 as a test CoverYourTracks also detects the same "Chrome PDF Viewer", despite it being broken when zooming in on large documents, so I don't believe they've completely replaced their PDF viewer, especially since it still looks the same and has a slightly different layout and user interface than the one in Chromium browsers.

So I don't know "what" they changed, only that they changed something that seems to have fixed PDF rendering for my admittedly niche use case and I just wanted to let y'all know in case this is something any of the rest of you have had issues with.

[Tidosho]

It wasn't a cache issue, was it? I know when cache gets corrupt all sorts of issues occur. Maybe during the update the browser refreshed itself?

[Gerowen]

On 17/07/2025 at 03:29, Tidosho said:

It wasn't a cache issue, was it? I know when cache gets corrupt all sorts of issues occur. Maybe during the update the browser refreshed itself?

Nah I've seen it happen on multiple machines for quite a long time now, and even when checking on this one rolling back to the old Firefox makes it blurry, updating to the new one makes it sharp.  I even deleted the cache and set up an empty profile on the old version to double check.