Firefox keeps asking if I want to open file with a certain program

Firefox keeps asking me if I still want to open a file type with a certain program, even though the checkbox that says Do this automatically for files like this from now on is checked. This window always pops up for this type of file. This has been an issue for me for several years and with different versions of Firefox.

I'm talking about a dialog window like this, but with different file type and options:

Checked or unckecked, the checkbox does nothing and this window always appears.

In the Applications tab, the file type is set to open with a specific application, and the window still appears.

How do I stop this madness?

Solution 1:

That behavior is usually because the file is served with a ContentDisposition: attachment response header. This is a long-standing bug in Firefox, due to an obstinate misinterpretation/misapplication of certain standards by Firefox developers. You will never stop the madness until that changes, and Mozilla fixes the bug. See for instance: https://bugzilla.mozilla.org/show_bug.cgi?id=453455.

Solution 2:

The posts here are 2014. As of August 2020, the same behavior continues to occur, and with simple pdf files. I have the setting for pdf files set to "Open in Firefox". But it behaves as if I've set it at "Always ask". The option button in the dialog box reflects the setting (Firefox vs. Adobe), but the appearance of the dialog box itself should not be happening. v. 79.0/Win 10.