Thunderbird always used to make suggestions for completing addresses in the TO box, using my local address books to find matching entries, once a letter or two had been typed into the TO box. After updating on April 25 2016 Thunderbird stopped finding matching addresses in my local address books and thus stopped making suggestions for completing the address. This is happening even though my OPTIONS are set to look in the local address books for matching entries. However, the sidebar display of my contacts works as it is supposed to, so that I can find the relevant addressee on the contact list and simply click on the entry to add the address to a TO box. So, Thunderbird is not having trouble finding my address books.