Every single time I download a .ris file, used for downloading/importing bibliographic references into citation management software such as EndNote, I tell Firefox to remember to open it with EndNote... and every time, it forgets. Going into the applications tab of preferences shows that, indeed, ris is not listed, though I've been telling it to save this preference for about a year now. Other reference file types are opening automatically with EndNote, as desireed, but Firefox will simply not learn .ris for some reason, and there's no option for me to manually put this into the list!