hello, firefox remembers the last download directory you chose during downloading from a certain domain (like facebook.com) & will offer the same folder as default option the next time you download from this site. the download folder doesn't depend on the filetype of your download... you might use an addon like the following to adapt this behaviour: https://addons.mozilla.org/firefox/addon/automatic-save-folder/

See also: *http://kb.mozillazine.org/Unable_to_save_or_download_files *https://support.mozilla.org/kb/Unable+to+download+or+save+files