Use ⌘ (OSX) or CTRL (Windows and Linux) and choose any two commits you like in log view. It does not matter what branch the commits belong to.
As a result you will see something like…
Displaying all changes between f03a18bf0370c62bb5fb5c6350589ad8def13aea and 4a4b176b852e7c8e83fffe94ea263042c59f0548
…down below.