Hi mart.verkerk, there are a number of reasons this could happen, starting from the filename assigned by the site. Does it help at all to set Windows to show all file extensions? This article has info on that setting: https://www.bleepingcomputer.com/tutorials/how-to-show-file-extensions-in-windows/ If you save the same file on another browser, is there more to the file name after the part Firefox saves under? And if so, was there a blank space between the parts?