The order in which you install add-ons, such as the provider for Google calendar and Exchange calendar support, matters. I've spent too long jiggering with add-

The order in which you install add-ons, such as the provider for Google calendar and Exchange calendar support, matters. I've spent too long jiggering with add-ons to get them to play nicely together. Once I have a functioning setup,I copy the profile wholesale from machine to machine. I use Thunderbird every day and have done for years.