If a context menu is raised on a buffer containing a modified version controlled file, then support for viewing the difference between the modifications with its previous commit is provided by the menu item “Ediff revision…”.
If Magit 4.4+ is installed, then different Magit commands depending on context are displayed. If the context menu is raised in a file buffer, then the menu item “Magit Dispatch…” (magit-file-dispatch) is shown, otherwise “Magit Status” (magit-status).