[https://support.mozilla.org/en-US/kb/where-find-and-manage-downloaded-files-firefox#w_change-where-downloads-are-saved_2 Change where downloads are saved]

Do you mean on Firefox for Android? Please see my reply in this thread: [https://support.mozilla.org/questions/1075416 How do I change the location of my Downloads folder?] Your Firefox reported to the forum that it is version 22, which is very old by now and has publicly disclosed security vulnerabilities. Can you run an updated version on your device? If not, consider using a different browser that may be more secure.