I'm migrating from SQL server to firebird, how do you convert the following MS SQL stored procedure to firebird?

CREATE STORED PROCEDURE insert_member
(
@username VARCHAR(25),
@password VARCHAR(25)
)
AS
BEGIN
BEGIN TRANSACTION
DECLARE @group_name VARCHAR(25);
INSERT INTO members (username, password) VALUES (@username, @password);
SELECT TOP 1 @group_name = group_name FROM groups ORDER BY last_modified;
INSERT INTO group_members (group_name, username) VALUES (@group_name, @username);

SELECT TOP(100) * FROM groups;
COMMIT;
END