A day after publishing Firefox 9 Mozilla released version 9.0.1 of its web browser that fixes vulnerability causing the software to crash. The flaw was caused by faulty patch included in version 9. In 9.0.1 the patch was removed.
Version 9 patched six security flaws. Four of them were rated „critical“, one „important“ and one „moderate“. Vulnerabilities allowed attacker to execute arbitrary code, launch DoS and XSS attacks.

Source: SC Magazine
23.12.2011