Whilst debugging my app, I noticed that Firebird v1.52 SS kept
abnormally terminating. I tracked it down to a recent trigger I'd added:

CREATE TRIGGER CONTACTS_CHANGED FOR CONTACTS ACTIVE AFTER INSERT OR
UPDATE OR DELETE POSITION 1 AS
begin
POST_EVENT 'CONTACT_CHANGED_' || old.contact_id;
end

Everytime this executed, the Firebird server terminated. It was my
mistake to refer to 'old.contact_id' in a trigger that is called after
an insert, but I'm surprised Firebird crashed.