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Open some special PDF-Files in FF with a non-standard program

  • 3 uphendule
  • 1 inale nkinga
  • Igcine ukuphendulwa ngu Sceptic

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My FF is set so that PDF files are downloaded automatically. In principle, this should remain that way. Now, however, I would like a few PDF files from my own disk to be opened directly instead. I have thought up a workaround for this - which unfortunately (STILL?) doesn't work properly:

1) The files in question (so far only one, as a test) are renamed *.PXX. 2) In Win I have defined that these *.PXX files should NOT be opened with my generally used PDF programme, but with Adobe Acrobat. This WORKS. 3) Now I had to define in FF that PXX should be treated differently from PDF. I haven't managed to do that yet - the files are still written to the download folder - RENAMED *.PDF 4) Meanwhile I found some (as far as I know) "unused" extensions in FF, amog them *.IRC. So, I renamed my *.PXX-file *.IRC and defined in FF that *.IRC-files should be opend by Adobe Acrobat. 5) NEVERTHELESS - disregarding this definition - the *.IRC-files are NOT opened but "downloaded" to the download-folder AND renamed *.PDF

Does anyone haven an idea?

All Replies (3)

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hello sceptic,

for what this response is worth:

from what i understand from microsoft is 1) ending some relationship with adobe acrobat and 2) the microsoft edge browser is designed with pdf capability and 3) ms office now creates pdf's without the use of pdf software.

i use wondershare and soda pdf software on win 10 to view and create pdf's. So the systems of managing pdf's are being re-written as we speak.


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Hi Sceptic, is Firefox opening these .PXX and .IRC files from a web server, or from your computer?

Web Server scenario

Normally, if a file has a .pdf extension, the web server will inform Firefox that its Content-Type is "application/pdf" and unless forced to show a download dialog, Firefox will follow the instructions on the Options page.

When serving a file with an unknown extension, the web server may inform Firefox that its Content-Type is "text/plain" which leads to a hideous text dump, or "application/octet-stream" which indicates a generic binary file. Firefox should show a generic Open/Save/Cancel dialog and won't save a specific action for "application/octet-stream" downloads because they could be anything. As an example: (I can suggest a workaround for Content-Type issues if that's the scenario.)

If you don't mind getting a download dialog but you want to avoid having Firefox "correct" the file extensions, try this:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box in the page, type or paste and pause while the list is filtered

(3) Double-click the preference to switch the value from true to false

Does that work for your files?


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Hi jscher2000, thank you for your detailed proposal. Let me first note that FF makes no difference if the IRC file comes from my disk or from a website. (

I changed the config-line as you proposed and that brought a small progress: The extension is no longer changed to pdf, but remains irc. Nevertheless the file is stored to my download folder (without opening the download dialogue!)


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