Possible Install Bug Rated 5 out of 5 stars
I recommend this add-on if you have a Gmail account or a Google Apps account and have more than the default folders. Follow the authors advice and use the correct version. Also, follow Google's recommended Thunderbird settings for Gmail accounts except for your account in Account Settings > Server Settings, under "When I delete a message:" "Move it to this folder:" select Trash. Possible bug follows:
I installed Gmail Buttons 0.5.1 on Thunderbird 17.0.2. I had to disable the add-on and re-enable it to get Gmail labels to show up in the message header. I don't know if this is a bug in the add-on, Thunderbird, interference from another add-on, or just a glitch.