This interface has no defined properties, but has properties based on the name of the columns in the SQL result from the statement it was accessed off of. For example, say you create a statement like so:
var statement = dbConn.createStatement("SELECT id, name FROM table_name");
The object would have two properties, id and name, that can be used to get the value of the column after you have called mozIStorageStatement.executeStep() like so:
while (statement.executeStep()) {
let id = statement.row.id;
let name = statement.row.name;
}