To enable the services, you need to copy the new version into the Applications folder (or a subfolder). To trigger an immediate rescan of Services, you can use bps tool from the command line:
/System/Library/CoreServices/pbs -existing_languages
Or, you can log out and log back in before the service becomes available.
In Finder, select one (or two) text file(s), and you should be able to find the Diff item in the Services menu (if it's not there, you may need to enable it in the Services Preferences).
http://www.dotfork.com/difffork/tutorial/#version-control-system-integration
Before 1.1.0, when a difference (a block or a line) is selected in file A, the corresponding difference in the counterpart text file (file B) is aligned vertically. This behavior is to help you identifier the differences in the counterpart text file.
Since 1.1.0, DiffFork supports "Block Guide" and "Scrolling in Sync", which makes auto-align no longer necessary. Now to align blocks, you need to press the Control key while you select the block. You can change the preferences to use other modifier keys.
Starting from this version, when you first use DiffFork, it runs in "Trial Mode". In this mode, DiffFork is fully functional and you can use it without registration for 15 individual days. There are no other limitations until the last day of your trial period.
First Public Release