Deleting the mimeTypes.rdf will reset all download actions to the default settings.

Type about:support in the address bar and press enter.

Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the mimeTypes.rdf file. Then rename or delete it. Restart Firefox.

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

FredMcD said

Deleting the mimeTypes.rdf will reset all download actions to the default settings. Type about:support in the address bar and press enter. Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox. Locate the mimeTypes.rdf file. Then rename or delete it. Restart Firefox.

---

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

The Show Folder. step is for Windows Firefox as it is Open Directory in Linux version of Firefox/SeaMonkey.

Selecting that choice would normally open a file picker window.

This window has for me some choices available in a Places list at the left and one of them is Recently Used.

Is that selection list missing for you?

Do you see this item list at the left if you save a downloaded file?

Thanks James and FredMcD, I tried to follow your advice but could not delete the file. It remains were it was and appears in "trash" simultaneously. Naturally the problem persists. If I rename the mimeTypes.rdf file will it not "confuse" the OS in a way that might paralyze firefox? My computer knowledge is poor but even in my advanced age (70) I am eager to learn and experience new fields.

cor-el: There is a selection list but no applications list.

I do see application list in the downloads folder when I right click - file name and - open with.