The problem did came from Firefox and was solved with Firefox 25 (tested on my own computer).
See: https://support.mozilla.org/en-US/questions/971876 http://support.mozilla.org/fr/questions/975586 ** Changed in: firefox (Ubuntu) Status: Confirmed => Fix Released -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1227497 Title: Missing group permissions on Firefox downloads To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1227497/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs