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Inbuilt PDF viewer not working

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I have Firefox 91.6.0esr (64-bit) on Windows. Previously I could access PDFs on a number of websites using the inbuilt PDF viewer. However now Firefox returns a save-as prompt.

I have checked the headers of some of these pdf pages and the header content-disposition: inline; filename=<abcdefg> is contained which I think should cause the PDF to be rendered in the browser but this is not happening. The pdfs on the same pages can be viewed using Edge.

Has the behavior of Firefox recently been changed?

I have Firefox 91.6.0esr (64-bit) on Windows. Previously I could access PDFs on a number of websites using the inbuilt PDF viewer. However now Firefox returns a save-as prompt. I have checked the headers of some of these pdf pages and the header content-disposition: inline; filename=<abcdefg> is contained which I think should cause the PDF to be rendered in the browser but this is not happening. The pdfs on the same pages can be viewed using Edge. Has the behavior of Firefox recently been changed?

Chosen solution

If the Content-Type is application/pdf and the Content-Disposition is inline (or omitted) then Firefox definitely prefers to use the built-in viewer. However, it's possible that at some point the instruction got switched on the Settings page. Could you try the steps in the following article to check on that and correct it if needed:

View PDF files using Firefox’s built-in viewer

Note: if Open in Firefox is missing as an option, one possible reason is a company policy against viewing PDFs in the browser. You can type or paste about:policies in the address bar and press Enter to load that page. Normally the "Active" policies panel says "The Enterprise Policies service is inactive." If yours lists anything related to PDFs, let us know.

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Seçilmiş Həll

If the Content-Type is application/pdf and the Content-Disposition is inline (or omitted) then Firefox definitely prefers to use the built-in viewer. However, it's possible that at some point the instruction got switched on the Settings page. Could you try the steps in the following article to check on that and correct it if needed:

View PDF files using Firefox’s built-in viewer

Note: if Open in Firefox is missing as an option, one possible reason is a company policy against viewing PDFs in the browser. You can type or paste about:policies in the address bar and press Enter to load that page. Normally the "Active" policies panel says "The Enterprise Policies service is inactive." If yours lists anything related to PDFs, let us know.

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Ahhh @Jscher2000,....seems that something reset my preference to view PDF in browser indeed! Silly me, I should have looked at that first.

Sorry i accidentally clicked the wrong thumbs button, should've been an up but got down instead :( Maybe I buy you beer instead?

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Glad you were able to fix it quickly, and no worries on the thumb.