Hello Barn, I don't know what your previous version of Thunderbird was (or the version of Office you're using), but this is "normal" behavior that is due to Microsoft and not Thunderbird. Some time ago (while Office 2010 was new), Microsoft decided that any Office document that was downloaded from the Internet or opened as an email attachment would default to "protected view" which is read-only. Read the page at http://www.askvg.com/how-to-disable-protected-view-in-microsoft-office-while-opening-email-attachments-or-downloaded-files/ to get tips & tricks on how to deal with this "feature." You can either click on the "enable editing" button or turn off protected view in Office 2010/2013 altogether. Hope this helps, Norio PS Here's my two cents: You should NEVER edit a file straight from an attachment; it is a temporary file and you could run into problems and lose any changes you make. It is better to save the attachment to a local drive and open it there.