Follow up from https://bugzilla.mozilla.org/show_bug.cgi?id=819839#c28 Luke Wagner says: " Initially EnsureAsmJSSignalHandlers was called lazily, so you could race if two workers happened to compile asm.js at the same time. Now it is called in JSRuntime::init, which I think we can assume happens-before other JSRuntime create. Thus, I'd be fine if you replaced all that junk with a simple static bool sHandlersInstalled = false; which was tested/set where lock.handlersInstalled()/lock.setHandlersInstalled() are called now. "

Comment on attachment 8340035 [details] [diff] [review] get-rid-of-InstallSignalHandlersMutex.patch Thanks!