Calendar invite display
Thunderbird has a setting in View > Message Body As > Plain Text. For normal email, this means only a stripped text representation of the original email body is shown to prevent Thunderbird form loading and/or executing malicious code.
Observation: Messages containing *.ics attachments are displayed in a HTML table.
Question: Does this mean that sending malicious code in an *.ics can circumvent the Plain Text setting safety measures?
Wšykne wótegrona (1)
What exactly is your definition of 'malicious code'? If you're talking about embedded JavaScript, Thunderbird does not run JavaScript code in email messages per definition, and it cannot be turned on manually either.
If you mean to click on a link to a malicious web site in an email, this would also be possible in plain text messages.