I often receive meeting invitations with the ICS attached invite file. When I accept the invite Thunderbird creates an event for the meeting in the calendar.
Once the event had been created there is no way to change the title of the event in Thunderbird. This is something needed because lots (all?) of invitations are sent from someone assigning titles from its own point of view. Invitations with titles like "Meet with SM" have no meaning to me and I will forget about the reasons of the meeting.
Now I have to add invitations to a Google calendar, go to Google calendar webapp, change the title of the invitation, return to Thunderbird and move the invitation to the right calendar.