Download handling default

At present, all my downloads (at least the PDFs) default to the Download folder. My default browser, Firefox, allows selecting the folder to which to download, but does not seem to offer an option to open the download without saving. I seem to recall being given such an option in the past, but haven't found such through the help selection in firefox or on the iMAC. I really don't want to save every download, and now am unable to view the PDFs on a genealogical site I use. I would much prefer to be given an option each time to either open or save when downloading. Is there some setting I'm missing either in Firefox or on the iMAC itself? OS High Sierra 10.13.6; 2017 21.5 ",