a. hitting the Enter key if the To: box is populated correctly
   b. clicking on the correct entry in the drop-down list
   c. scrolling down to the entry and pressing Enter.

After Thunderbird [running on Windows 8.1] updated from v. 30 to 31.0, the To: line in email addresses pulled from my Address Book turns and remains red, rather than changing to black. _This issue is dependent on the typing speed while entering the first characters of an email address_ and only occurs when typing slowly. To replicate: 1. Type a few letters from the email address in the Address Book, typing s l o w l y. Choose an entry for which there is more than one name or email address beginning with the same same letter. (Collected Addresses was the source in my tests.) 2. Select one of the entries shown, either by a. hitting the Enter key if the To: box is populated correctly b. clicking on the correct entry in the drop-down list c. scrolling down to the entry and pressing Enter. 3. Observe that while typing, on the second or subsequent letter entered the To: text changes from black to red.