If you are stil having problem viewing, downloading and uploading attachment via email using opera, here is a simple ting to do؛
1. Login to your gmail account
2. Just open your address bar ant enter this؛ mail.google.com/mail/?ui=html&zy=h
3. This will open your gmail for you as if you are on a computer and thats all you can view all your attachments.
NOTE: make sure you copy the above address and keep it safe. That is mail.google.com/mail/?ui=html&zy=h