Setting originalContent and changedContent didn't work for me. I changed these two lines:
original = $(settings.originalContainer, this).text();
changed = $(settings.changedContainer, this).text();
... to
original = settings.originalContent || $(settings.originalContainer, this).text();
changed = settings.changedContent || $(settings.changedContainer, this).text();
... to use originalContent and changedContent when set, rather than originalContainer and changedContainer.