Problem: When a match within the page is not found, the Find dialog doesn't
respond with a usable message (such as "Term not found" or "Find could not
find %word").

How to repeat: 
1. Ctrl + F
2. Enter a search term that doesn't exist in the document

All you notice when there is no match is that the Next button becomes
greyed out. However, the user doesn't get a useful message back (so how
would a user know the find failed?).

Suggestions for modification:
0. Display a message
1. Upon greying out the Next button, move the default button to the Close
button, so if the user hits the Enter/Return key, the find dialog box closes.