Try this addon:

• https://addons.mozilla.org/en-us/thunderbird/addon/addressbooktab/

I have Thunderbird 24.6 installed and the addressbooktab utility won't load. Is there something I should be doing different?

How to install an addon:

• https://support.mozilla.org/en-US/kb/add-ons-and-extensions-faq#w_how-do-i-install-an-add-on

I have installed it per the instructions and restarted TB, but I still don't find a way to have the address book appear as a tab at the top of Thunderbird.

It adds a button that can be put in toolbars and that open the addressbook in a new tab.

View > Toolbars > Customize or 3bar menu icon > Options > Toolbar Layout

Drag addressbook tool onto toolbar.

Found it! Thanks much. I went to "tools/add-ons/extensions/options" and checkmarked the boxes.

Thansk again!