This is an issue dating back about 15 years. Sites are not supposed to have spaces in an unquoted filename when sending a download header and Mozilla decided not to follow other browsers that fill in the gap. http://kb.mozillazine.org/Filenames_with_spaces_are_truncated_upon_download Can you suggest to the site that they fix it? It should be pretty easy for them, either by adding quotation marks around the file name or replacing spaces with underscores. There are plenty of recipes online: [https://www.google.com/search?q=content-disposition+filename+spaces+firefox+site:stackoverflow.com content-disposition filename spaces firefox site:stackoverflow.com - Google Search]