How to prevent Thunderbird from updating automatically?
Referring to your second question:
Avoiding automatic updates for a specific package
Install synaptic package manager if you haven't done so already
sudo apt-get install synaptic
Open it up and search for the package in question, e.g. thunderbird. Mark the package you want to modify and head to Package --> Lock version.
Do the same for all thunderbird related packages and thunderbird will not get upgraded until you remove the version lock flag.