The browser engine in Mozilla Firefox before 3.0.12 and Thunderbird allows remote attackers to cause a denial of service (memory corruption and application crash) or possibly execute arbitrary code via vectors related to (1) the frame chain and synchronous events, (2) a SetMayHaveFrame assertion and nsCSSFrameConstructor::CreateFloatingLetterFrame, (3) nsCSSFrameConstructor::ConstructFrame, (4) the child list and initial reflow, (5) GetLastSpecialSibling, (6) nsFrameManager::GetPrimaryFrameFor and MathML, (7) nsFrame::GetBoxAscent, (8) nsCSSFrameConstructor::AdjustParentFrame, (9) nsDOMOfflineResourceList, and (10) nsContentUtils::ComparePosition.