I asked help already in mozilla forums:
[...] it seems, that since the update to v31 Thunderbird does not open attachments as read-only (at least on my installs) and you can edit and save attachments (in my case libreoffice documents into the /tmp directory). Unsurprisingly - after restart I have lost a days work now.
And got the following answer:
As far as I can recall, that functionality has not changed, at least not in the Windows version of Thunderbird. TB has always opened messages in the Temp directory using the associated "helper program." Whether that file was opened in read-only mode or not would seem to be up to that external program or the OS.
It seems that Ubuntu (14.04) handles this somehow differently. What should I do to restore the previous behaviour, i.e. force thunderbird to open attachments as read-only?
