you have to do two things, first set these three settings as follows (this is in Java, but I think you will be able to translate this into python :-):
profile.setPreference("browser.download.dir", "c:/yourDownloadDir");
profile.setPreference("browser.download.folderList", 2);
profile.setPreference("browser.helperApps.neverAsk.saveToDisk", "application/csv, text/csv");
-, , mime. - .
EDIT:
, MIME- Chrome, Ctrl + Shift + I (Cmd + Alt + Mac OS), "" . - :
