Comment 11 for bug 1914147

CacheIO Thread holds mRCWNLock and try to dispatch SyncRunnable on the main thread:
                              45 mozilla::net::nsHttpChannel::OnCacheEntryCheck(nsICacheEntry*, nsIApplicationCache*, unsigned int*) + 2485 (XUL + 7218629) [0x107e7d5c5] 1-45
                                45 mozilla::net::nsHttpChannel::OpenCacheInputStream(nsICacheEntry*, bool, bool) + 1539 (XUL + 7225683) [0x107e7f153] 1-45
                                  45 mozilla::net::CacheEntry::GetSecurityInfo(nsISupports**) + 197 (XUL + 41189653) [0x109ee3115] 1-45
                                    45 NS_DeserializeObject(nsTSubstring<char> const&, nsISupports**) + 131 (XUL + 6224003) [0x107d8a883] 1-45
                                      45 nsBinaryInputStream::ReadObject(bool, nsISupports**) + 274 (XUL + 5336850) [0x107cb1f12] 1-45
                                        45 nsCOMPtr_base::assign_from_helper(nsCOMPtr_helper const&, nsID const&) + 44 (XUL + 5114444) [0x107c7ba4c] 1-45
                                          45 nsCreateInstanceByCID::operator()(nsID const&, void**) const + 42 (XUL + 5481626) [0x107cd549a] 1-45
                                            45 nsComponentManagerImpl::CreateInstance(nsID const&, nsISupports*, nsID const&, void**) + 183 (XUL + 5470679) [0x107cd29d7] 1-45
                                              45 nsresult mozilla::psm::NSSConstructor<mozilla::psm::TransportSecurityInfo>(nsISupports*, nsID const&, void**) + 56 (XUL + 84060120) [0x10c7c57d8] 1-45
                                                45 EnsureNSSInitializedChromeOrContent() + 583 (XUL + 21727959) [0x108c53ad7] 1-45
                                                  45 mozilla::SyncRunnable::DispatchToThread(nsIEventTarget*, bool) + 156 (XUL + 5904060) [0x107d3c6bc] 1-45

The main Thread is waiting on the mRCWNLock.

Kershaw, do I recall correctly that we have this SyncRunnable only because of some test? EnsureNSSInitializedChromeOrContent should always be called on the main thread.

Dana, do you know whatt has change recently