This line https://github.com/phpbb/phpbb/blob/master/tests/test_framework/phpbb_functional_test_case.php#L418 perform the checks

$this->assertGreaterThan(0, $crawler->filter('.submit-buttons')->count());

.submit-buttons fieldset does not exist in 3.3 confirmation page.

Also here https://github.com/phpbb/phpbb/blob/master/tests/test_framework/phpbb_functional_test_case.php#L420 'Enable' button doesn't exist on comfirmation page too (not it is called 'Yes').

Hence test fails with

Failed asserting that 0 is greater than 0.

/home/travis/build/phpBB3/tests/test_framework/phpbb_functional_test_case.php:418

/home/travis/build/phpBB3/tests/test_framework/phpbb_functional_test_case.php:112

and extension is not installed, so all other functional extension tests fail.

P.S. It looks like phpbb_ui_test_case.php has the same issue.