Lets say I have 2 files opened in SE and I want to diff them with a minimum amount of clicks.
One way to do it would be if I right click on a tab of the first file and there is an option "Use this file for left pane of compare".
Then I right click on the tab of the 2nd file and choose an option "Compare this file to <name of file previously clicked>".
After this DIFFZilla (or perhaps an external diff tool that one could specify somewhere) would pop up allowing a comparison.
I use a similar technique as this for Beyond Compare (files and directories) and windows explorer/dolphin right click menus.
