Goto "view all versions" on the bottom of this add-on homepage. Download the experimental version 1.2.1 dated 2011-07-01, 329.7 kB. Works perfect with my v5.0 Thunderbird among about 30 other add-ons. Display-Contact-Photo is perfect with intranet domain pictures to avoid wrong addressed extranet e-mails.
This review is for a previous version of the add-on (1.2).