Thunderbird & Google Calendar read-n-write 2-way sync

Simply follow this Google instructions, which basically says:

0. install Lightning (add-on) in Thunderbird
then

1. Open the Sunbird application and select File > New Calendar.
2. Select On the Network and click Next.
3. Select the CalDAV format option.
4. In the Location field, enter [ https://www.google.com/calendar/dav/ [ your Google Calendar ID ] /events ] and click Next.Your Google Calendar ID for your primary calendar is just your email address, but for all other calendars the Calendar ID will be in the form of [ long string of characters]@group.calendar.google.com. You can get the Calendar ID by clicking the down arrow next to your calendar at calendar.google.com and selecting 'Calendar Settings'.
   
   Be sure to use https in your URL, as an http address will not work.
5. Enter a name and select a color for your calendar.
6. In the pop-up screen, enter the following information:Username: This is the complete email address you use with Google Calendar (including the part after the @ sign). If you're using Google Apps, be sure to enter your Google Apps email address.
   Password: This is the password you use to sign in to Google Calendar
7. Click OK.

Instructions were made originally for Mozilla Sunbird, but also work with Thunderbird+Lightning, although considered an experimental feature.