The account manager window

The account wizard that you see when you create a new account or when you start Instantbird the first time.

The main Contacts window including the list of all Contacts and the Conversations on Hold.

The conversation window or thing displayed in the conversation itself

Official add-ons from Instantbird team found at hg.instantbird.org/addons (this is not for all add-ons, only ones provided by the developers of Instantbird!).

Anything that doesn't fit in any of the components

The preferences window