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Lolu chungechunge lwabekwa kunqolobane. Uyacelwa ubuze umbuzo omusha uma udinga usizo.

I am trying to update a product that uses .DFU. Firefox is saving the file as a PDF. How do I get it to download it in its native .DFU? Thanks, Mike

  • 7 uphendule
  • 1 inale nkinga
  • Igcine ukuphendulwa ngu jscher2000

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I am trying to upload jpeg file to show....but it isn't uploading either file type. Sorry.

Again, the file is a .dfu type. Firefox can't download it in that format. It is asking me to pick a file type. There is none on the list that work for .dfu.

Any ideas?

Thanks in advance

All Replies (7)

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Have you tried using; 'Save As' ?

Once the file is downloaded, why not change its extension?

Are you using Firefox download or a download manager? The filename/extension should not get changed.

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Hi Fred.

Thanks for the idea. I have tried that too. Firefox wants to save it as a type. I can go into the file properties (right click) and see it saved that way even though the file itself still had the extension .dfu.

Regarding what application is downloading it, I can't say for sure. I poked around a bit and didn't see anything relevant. FYI, I am just clicking on the link showing up in that browser page.

Where would I find which is being used and where I might change or modify it?

Thanks for your help! Mike

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Hi Mike, what is the content you are trying to download?

On Windows, if you put quotation marks around the full file name in the download dialog, no extra extensions should be added. For example:


To check for extra file extensions, set Windows to always show them:

Usually if Firefox perceives a download as a PDF file, that is because the server sent the content-type application/pdf. However, it's also possible that Firefox learned that a generic type such as application/download is also a PDF.

I can give you the steps to erase what Firefox has learned about different content types, but more importantly, if you don't know what the .dfu file is, be very cautious that it is not malware masquerading as something useful. If in doubt, contact the software vendor.

The following is written for recent versions of Firefox. The handlers.json file did not exist in older versions.

Sometimes the settings file that stores download handling preferences becomes corrupted. You can rename the file and have Firefox rebuild it. Here's how:

Open your current Firefox settings (AKA Firefox profile) folder using either

  • "3-bar" menu button > "?" Help > Troubleshooting Information
  • (menu bar) Help > Troubleshooting Information
  • type or paste about:support in the address bar and press Enter

In the first table on the page, on the Profile Folder row, click the "Open Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Leaving that window open, switch back to Firefox and Exit, either:

  • "3-bar" menu button > Exit/Quit
  • (menu bar) File > Exit (or Firefox > Quit)

Pause while Firefox finishes its cleanup, then rename handlers.json to something like handlersOLD.json. If you see a file named mimeTypes.rdf, rename that one to mimeTypesOLD.rdf.

Start Firefox back up again. Any improvement?

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Hi jscher2000,

Thanks for the detail response. Unfortunately, that didn't work either.

I am running Firefox ESR 52.9.0 (64-bit) so I can continue to use Silverlight.

Perhaps that is an issue with that solution.

Thanks, Mike

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Hi Mike, I went back and read your earlier replies, and you had said:

HappyGuyInMN said

I can go into the file properties (right click) and see it saved that way even though the file itself still had the extension .dfu.

I had suggested making sure you see all file extensions to rule out an additional .pdf extension on the file (

If it's still just a .dfu extension but Windows thinks it is an Adobe Acrobat document, you may need to re-associate it to the correct program at the Windows level.

Or maybe it's easier to download the .dfu file using Edge if that works normally.

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OK. Thanks jscher2000.

Let me try and upload pics again. This didn't work the other day.

The file on the desk shows as a PDF with a .dfu extension.

Right clicking the file brings up the first pic. I can't change the open with because none of my apps open .dfu and there is no app in the store that opens a .dfu.

THat help now?

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I would check the manufacturer's instructions for how that file is supposed to be used. It only needs to be associated with the "correct" application if it's meant to be launched by double-clicking. If it's meant to be read into another application using a menu command, or if it's a firmware update you place at the base level of an SD card (or similar method), then the wrong association isn't a problem, just a distraction.