The default page showing the messages history between two users is not nice. Because of how it is split into two visual columns, they can become quite narrow on smaller screens. If the history is longer, I find it quite difficult to follow who said what (was it me or they?) at the bottom of the screen.

I came up with a theme improvement that renders the page in kind of similar way how some chat clients do it. Additionally, a small core hack allows us to display user pictures in messages themselves, making it easier to follow the discussion.

If this improvement is accepted well at moodle.org sites, we can submit it as a Moodle core default feature.