PDFs download only as .pdf.part files in Downloads folder and extension must be renamed

Firefox 157.0 (aarch64) macOS Tahoe 26.7.1 When I click on the link to a PDF to open it in Firefox and click on the Save icon in the file viewing UI (see attached image pdf-save-icon.png) to save it to my local device, no File Save dialog box opens and nothing happens. If I right click on the link to the file instead of opening the file, the file is saved silently to the Downloads folder with a name that ends in .pdf.part (see attached image filename.png). That typically indicates a partial, failed download, but in this case, if I remove the .part from the filename, the result is a viable PDF.