Files previously downloaded by earlier versions of Firefox as .webp cannot be opened by 115.19.0esr. Firefox keeps asking what application to use, and I have selected Firefox. When I OK the selection, it opens a blank screen with the same question (what application to use). This goes on forever, opening a new blank tab again and again, each with the same question about what application to use. My old Mac operating system 10.13.6 retains its original version of Preview installed, and of course, that version of Preview does not know how to open .webp files.