Open with Notebook (default)"

I download Endnote .ris reference files every day, and have done for decades. Endnote supplies a parsing tool that imports the data into the database. But it has just stopped working. In the import dialog box, the message that comes up on downloading a ris file is: "what should Firefox do with this file? Open with Notebook (default)" Well down the dropdown option list I can choose to open with Endnote, so I clicked on "Do this automatically for files .." then chose the Endnote option. Which works, but it doesn't stick. If I go to the Options page>Applications>ris, nothing comes up. If I choose >Endnote, the suggested option is to open every Text file with Endnote - not a good idea. Has something gone wrong with Firefox or with Endnote settings? Thank you