I have installed Getright plugins for Mozilla (http://www.getright.com/opera.html) I use IMAP over SSL. When I receive an email with an attachment try to "Open" it, getright is fired up and messes things up. "Save as" and "Save all" work just fine. This works every time but not with every kind of attachment. Zip files "Open" just fine. Doc, PDF and RTF files do not. If both types are attached to the same email message, one attachment "open"s, the other does not.
The getright plugin is a workaround and that cause this problems (and a few other) *** This bug has been marked as a duplicate of 58744 ***