You should be able to download (no option to upload that I know of, though).
Go for instance to
ftp://ftp.mozilla.org/pub/
You should be able to download the files from there just using firefox
(for instance ls-lR.gz). If the file is a web page or plain text, it
will be rendered by default, but you could still store it with 'Save as'
or with the context menu from the file list.