Should be built-in Rated 1 out of 5 stars
I don't undestand why this functionality is not built-in in TB and why an extension is needed. It was built-in in former Outlook Express (but does not exist in other more recent MS equivalent programs).
The last stable version of Contacts Sidebar (0.7.1, 2007) was compatible with TB3 and the last stable TB is now version 6 ! In that cas, why does Mozilla still mention it in this addons page ?