This is easy to confirm:

openxs@ao756:/tmp$ mysql -uroot -proot test
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Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> select @@innodb_file_format;
+----------------------+
| @@innodb_file_format |
+----------------------+
| Barracuda            |
+----------------------+
1 row in set (0.00 sec)

mysql> explain SELECT COUNT(DISTINCT `t1`.`id`) FROM `t1` INNER JOIN `t2` ON `t2`.`id` = `t1`.`f1` LEFT OUTER JOIN `t3` ON `t3`.`f1` = `t1`.`id` AND t3.f3 IS NULL AND `t3`.`f4` = 'Entry' LEFT OUTER JOIN `t3` `thumbnails_t3` ON `thumbnails_t3`.`f3` = `t3`.`id` WHERE `t1`.`f2` IS NULL AND `t1`.`f3` = 85260 AND (t1.f3 = 85260 AND t2.f2 IS NULL);
+----+-------------+---------------+--------+---------------+---------+---------+------------+------+-------------+
| id | select_type | table         | type   | possible_keys | key     | key_len | ref        | rows | Extra       |
+----+-------------+---------------+--------+---------------+---------+---------+------------+------+-------------+
|  1 | SIMPLE      | t1            | ref    | f3            | f3      | 4       | const      |  511 | Using where |
|  1 | SIMPLE      | t2            | eq_ref | PRIMARY       | PRIMARY | 8       | test.t1.f1 |    1 | Using where |
|  1 | SIMPLE      | t3            | ref    | f3,f1         | f3      | 9       | const      |    1 | Using where |
|  1 | SIMPLE      | thumbnails_t3 | ref    | f3            | f3      | 9       | test.t3.id |    1 | Using index |
+----+-------------+---------------+--------+---------------+---------+---------+------------+------+-------------+
4 rows in set (0.00 sec)

mysql> explain SELECT COUNT(DISTINCT `t1`.`id`) FROM `t1` INNER JOIN `t2` ON `t2`.`id` = `t1`.`f1` LEFT OUTER JOIN `t3` FORCE INDEX(f1) ON `t3`.`f1` = `t1`.`id` AND t3.f3 IS NULL AND `t3`.`f4` = 'Entry' LEFT OUTER JOIN `t3` `thumbnails_t3` ON `thumbnails_t3`.`f3` = `t3`.`id` WHERE `t1`.`f2` IS NULL AND `t1`.`f3` = 85260 AND (t1.f3 = 85260 AND t2.f2 IS NULL);
+----+-------------+---------------+--------+---------------+---------+---------+------------------+------+-------------+
| id | select_type | table         | type   | possible_keys | key     | key_len | ref              | rows | Extra       |
+----+-------------+---------------+--------+---------------+---------+---------+------------------+------+-------------+
|  1 | SIMPLE      | t1            | ref    | f3            | f3      | 4       | const            |  511 | Using where |
|  1 | SIMPLE      | t2            | eq_ref | PRIMARY       | PRIMARY | 8       | test.t1.f1       |    1 | Using where |
|  1 | SIMPLE      | t3            | ref    | f1            | f1      | 628     | test.t1.id,const |   11 | Using where |
|  1 | SIMPLE      | thumbnails_t3 | ref    | f3            | f3      | 9       | test.t3.id       |    1 | Using index |
+----+-------------+---------------+--------+---------------+---------+---------+------------------+------+-------------+
4 rows in set (0.00 sec)

mysql> flush status;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT COUNT(DISTINCT `t1`.`id`) FROM `t1` INNER JOIN `t2` ON `t2`.`id` = `t1`.`f1` LEFT OUTER JOIN `t3` FORCE INDEX(f1) ON `t3`.`f1` = `t1`.`id` AND t3.f3 IS NULL AND `t3`.`f4` = 'Entry' LEFT OUTER JOIN `t3` `thumbnails_t3` ON `thumbnails_t3`.`f3` = `t3`.`id` WHERE `t1`.`f2` IS NULL AND `t1`.`f3` = 85260 AND (t1.f3 = 85260 AND t2.f2 IS NULL);
+---------------------------+
| COUNT(DISTINCT `t1`.`id`) |
+---------------------------+
|                       512 |
+---------------------------+
1 row in set (0.00 sec)

mysql> show status like 'Handler_read%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 0     |
| Handler_read_key      | 514   |
| Handler_read_last     | 0     |
| Handler_read_next     | 512   |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 0     |
+-----------------------+-------+
7 rows in set (0.00 sec)

mysql> flush status;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT COUNT(DISTINCT `t1`.`id`) FROM `t1` INNER JOIN `t2` ON `t2`.`id` = `t1`.`f1` LEFT OUTER JOIN `t3` ON `t3`.`f1` = `t1`.`id` AND t3.f3 IS NULL AND `t3`.`f4` = 'Entry' LEFT OUTER JOIN `t3` `thumbnails_t3` ON `thumbnails_t3`.`f3` = `t3`.`id` WHERE `t1`.`f2` IS NULL AND `t1`.`f3` = 85260 AND (t1.f3 = 85260 AND t2.f2 IS NULL);
+---------------------------+
| COUNT(DISTINCT `t1`.`id`) |
+---------------------------+
|                       512 |
+---------------------------+
1 row in set (1.04 sec)

mysql> show status like 'Handler_read%';
+-----------------------+--------+
| Variable_name         | Value  |
+-----------------------+--------+
| Handler_read_first    | 0      |
| Handler_read_key      | 514    |
| Handler_read_last     | 0      |
| Handler_read_next     | 512512 |
| Handler_read_prev     | 0      |
| Handler_read_rnd      | 0      |
| Handler_read_rnd_next | 0      |
+-----------------------+--------+
7 rows in set (0.00 sec)