For those with widescreen monitors, I have a addition to the above process that I find more efficient.
1. Save a second copy of your library under a different name
2. Open this copy, along with the original.
3. Use the “Windows” menu to tile the two libraries vertically.
4. Use the method specified in Jason’s post above in the copied library.
5. Remove duplicates using the original library.
This allows you to work with the original library, while maintaining the highlighted duplicates in the copied library, thereby eliminating the need to keep rehighlighting.