If you’ve worked with WinMerge, FileMerge is going to take some getting used to because the key commands mean the opposite of what you’ve become accustomed to.

The up and down arrow keys still take you to diffs up and down the file. How do you select which diff to use? I couldn’t find documentation for this key command, but experimentation revealed that Command-RightArrow and Command-LeftArrow are your boys. Thing is, they differ. WinMerge has that a right arrow takes a diff from the left and moves it into the file on the right. This is totally logical to me. FileMerge, on the other hand, has Command-RightArrow mean that the merged file will use the diff on the right. I know that has a logic as well, but I always picture arrows as moving things, so the WinMerge paradigm just makes a little more sense.