Rated 5 out of 5 stars
Context Highlight is a neat little add-on that, unlike Cmd+F (find), has the ability to highlight multiple selections simultaneously - and in different colors!
Just select another word or phrase, hold the Control key, right click and select "highlight word" or "...phrase." You can do this multiple times, and each new group will be highlighted in a different color. Right click and choose "clear highlighting" to remove.
Very useful. Thanks!