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PDF viewer extremly slow

Making moves

Since a few versions ago, the pdf viewer built into Firefox has been extremely slow for some documents.

Unfortunately, I have not yet been able to determine what the slowly displayed PDF files have in common.

It is not due to the size. Even PDF documents with only one page sometimes take up to 4 seconds until the PDF page is displayed.

It's not because of my computer. Intel Xeon, 32 GB RAM

The PDF is embedded with the HTML tag object.



@Entwicklungcan you share one or more PDF documents where you're experiencing this slowness?

Hello Marco,

thank you for asking.

The performance problem only arose under Microsoft Windows 10. The problem no longer occurs with version 11, which is now in use.



I am experiencing a similar issue. My Ryzen 7 processor should be sufficient for the task at hand. I have a 2MB PDF with 26 pages. When I open this document and immediately scroll down to the last page, it takes 20 seconds to load. In Okular PDF viewer, however, it is nearly instantaneous. Conversely, I have PDF files exceeding 5MB that load nearly instantaneously in Firefox.

I can provide you the pdf file, but I don't want to post it to the internet.

It would be ideal if you can share the document with us.

You can send it to my Mozilla email: mcastelluccio AT

Making moves


as I have already stated, the problem only existed under Windows 10, not under Windows 11, although I cannot explain this.

The problem with the PDF file also only existed with Firefox. All other browsers (Edge, Opera, Chrome) displayed the same file quickly.

Unfortunately, I cannot provide the file with which I discovered the problem.

When I tested it again with the latest Firefox version, I could no longer reproduce the problem under Windows 10.

It is therefore possible, that the problem has already been solved (by Mozilla or Microsoft).


@Entwicklung yes, I was asking the other user, @leinad .

Ohh sorry. I did not get any notifications. I will send you the document within the next days. The problem is still there in version 127.

Making moves

I have a similar problem in Windows 11 with a pdf (original svg file) embedded in a WordPress website.

Here's the page:

In Google Chrome it opens instantly.

Making moves

I didn't notice this in a version for PC, but PDF viewer in my Firefox for Android is slow. When I open a file from the internet and try to zoom in something there, viewer starts rebuilding it. Often it's faster to download the file and then open it with another app.


The slowness is related to these PDFs which contain some huge images. We'll see if we can implement some optimizations for such cases.