This indicates an attack attempt against a Memory Corruption vulnerability in Mozilla products.
The vulnerability is caused by an error when the vulnerable software handles javascipt with malicious BumpChunk objects. It allows a remote attacker to execute arbitrary code on vulnerable systems via sending a crafted web page.
Mozilla Firefox before 28.0
Mozilla Firefox ESR 24.x before 24.4
Mozilla Thunderbird before 24.4
Mozilla SeaMonkey before 2.25
System Compromise: Remote attacker can gain control of vulnerable systems.
Refer to the vendor's web site for suggested workaround.