Thanks to Papal Rated 5 out of 5 stars
Love this add on, but not compatible with TB 9.
Appears to work if you do the following: (keep in mind that this technique tells TB that Contacts Sidebar is compatible. No guarantee that it actually is):
1. Download the add on to your download folder as you normally would
2. Change the extension from .xpi to .zip (you will get a warning -- allow the change)
3. Unzip the zip folder
4. Open the file install.rdf
5. Move the cursor to the extreme right off the page and change the <em:maxVersion>8.9.*</em:maxVersion>
6. Save the file install.rdf. and exit
7. Change the extension name back to .xpi.
8. Install into TB as usual from Add On menu