In order to synchronize Google Calendar with Thunderbird you need to download and install both the lightning add-on and the provider add-on.

1. Information on Lightning: https://addons.mozilla.org/en-US/thunderbird/addon/2313
2. Information on Provider: https://addons.mozilla.org/en-US/thunderbird/addon/4631

Installing Lightning

1. Right-click (Control-click on Mac) the download link and choose "Save Link As..." to download and save the .XPI file to your your hard disk
2. In Mozilla Thunderbird, under the "Tools" menu, open the "Add-ons Manager"
3. Click the "Install" button, locate and select the .XPI file you downloaded in step 1, and click "OK"
4. Restart Mozilla Thunderbird

Installing Provider

You can obtain the provider from addons.mozilla.org. It is available for Sunbird and Lightning.

Note it is recommended to use the latest version of Sunbird or Lightning together with the latest Provider for Google Calendar version.

If you are using the latest nightly versions of Sunbird/Lightning, please use a comm-central version from ftp.mozilla.org

Configuring access to Google Calendar

Retrieving your private XML URL

To access your calendar data, you need to retrieve your private XML URL from the Google Calendar UI. If you are not sure how, follow these steps:

1. Open your Google Calendar if you use Google Apps, you will want to use your custom URL that was provided to you.
2. Click on the Settings link located in the box at the left of the page.
3. Click on the calendar you want to use with Thunderbird Lightning or Sunbird.
4. Click on either of the two XML buttons shown at the bottom.

Note that the provider does not directly use your private url. The Calendar is still accessible when you reset your private url.

You may now use this url as the Location when clicking File > New > Calendar > On the Network > Google Calendar in Sunbird/Lightning. 

Setting up Thunderbird

You can do this by clicking on the following Menu item:

File -> New -> Calendar…

Upon clicking the New Calendar menu item, another window will appear. The first option is the location of your Calendar - select “On the Network” and click Next.

The next option allows you to specify the Format of the Calendar, select the “Google Calendar” radio button (if you don’t have a Google Calendar radio button, make sure your Provider Extension is installed correctly). In the location input box, paste in your Google Calendar Private Address XML Feed that we extracted above, and click Next.

The next window asks you to give your new Calendar a Name and a Color.  This is personal preference.

Finally you will have a “Google Calendar Login” window which will ask for your Google Account login. If you only have a single Google Calendar, Provider will have automatically extracted your username from the XML feed you just specified.