When downloading an attachement with spaces in the file name is truncated to the first space in the file name.

Some people have reported this a bug against Firefox, however they have said that they won't fix it as it happens when one does "not properly escape the spaces in the HTTP headers it sends...". See:
https://bugzilla.mozilla.org/show_bug.cgi?id=252309
https://bugzilla.mozilla.org/show_bug.cgi?id=221028