Mozilla Firefox 3.0.8 and earlier 3.0.x versions allows remote attackers to cause a denial of service (memory corruption) via an XML document composed of a long series of start-tags with no corresponding end-tags. NOTE: it was later reported that 3.0.10 and earlier are also affected.
https://www.exploit-db.com/exploits/8306
https://exchange.xforce.ibmcloud.com/vulnerabilities/49521