The IsCSSWordSpacingSpace function in Mozilla Firefox before 16.0, Firefox ESR 10.x before 10.0.8, Thunderbird before 16.0, Thunderbird ESR 10.x before 10.0.8, and SeaMonkey before 2.13 allows remote attackers to execute arbitrary code or cause a denial of service (out-of-bounds read) via unspecified vectors.