I promised to post any solution I found to the above question, and as I've been unable to connect to the previous thread, I've taken the liberty of starting a new one. What worked for me was to change the default settings for «Open Document» services under «Applications» in the «Firefox Preferences» (this on my 64-bit Ubuntu setup ; in Windows, it is is called «Firefox Options» from «Use OpenOffice.org Plug-in» to «Use soffice». The odd thing is that this procedure opens appended documents to email messages in, say, Chrome/Chromium as well as Firefox. I haven't tested as yet in Opera....
Henri
