It needs just a small refinement, to become perfect.
Currently, the problem is that it breaks the preview functionality.
When a message has a document or a picture as an attachment, if i click "Preview",
the pane for preview appears at the right of message's body but it's blank.

[Edit]
Unfortunately, things are even worse..
It breaks also the "Contacts" functionality. When i click the "Contacts" button at the top-right,
the right side expands towards the left, but it's also blank. So, it's not possible to see my
contacts, edit, add, delete, etc.
If i disable this extension, both of these issues get gone.