Attachcments with spaces in the filename get truncated when downloading in Firefox

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