Thank you for the link. Apart from the reference to a "gear" icon that doesn't exist (not even in the screen shot), the instructions are easy to follow and they work.
However, instead of disabling every Thunderbird User's mail client without notice, it would have been far better to include a message in the update notice explaining what would happen after the Avast update is installed, and what to do. So, not impressed Avast - unprofessional.
