I don't understand. Where do you want them to open? Do you want to download them and if so, what will you read them with?

Have you a replacement for Adobe Acrobat Reader.

I don't understand. Where do you want them to open? Do you want to download them and if so, what will you read them with? Have you a replacement for Adobe Acrobat Reader.

I want to open them with other programs than within Firefox or Adobe.

go to the other programs and set one of them them as default

Also, please see this support article: View PDF files using Firefox’s built-in viewer.

OK there seems to be a built-in Firefox pdf viewer. However, in my settings it says 'always ask' and not 'open with firefox'.

I do not want to specify my other pdf viewer that I use because I want it to ask me whether to open it or download it.

It seems that Firefox does not do what I am telling it to do by having chosen 'always ask'.

This must be a bug, can anyone report it please?

With "Portable Document Format (PDF)" set to "Always Ask" on the Options page, you should get 3 choices for PDFs in Firefox 78:

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I assume that part is working as you want. But the problem is the "Open with" option?

If your settings are set to always ask, Firefox will look for other Windows programs that handle PDF's, like Adobe or Foxit Reader. But if no such programs are registered, Firefox will automatically default to the built in PDF viewer.
You need at least one registered PDF viewer in order to be given a choice.

THANK YOU!