Bug 826029 - Assertion in mozPoisonWriteMac due to Mac camera code trying to write a defaults file on exit | Assertion failure: ok, at ../../../xpcom/build/mozPoisonWriteMac.cpp:90. r=ehsan.

browser/app/nsBrowserApp.cpp

@@ -111,6 +111,7 @@ XRE_SetupDllBlocklistType XRE_SetupDllBlocklist;
 XRE_TelemetryAccumulateType XRE_TelemetryAccumulate;
 XRE_StartupTimelineRecordType XRE_StartupTimelineRecord;
 XRE_mainType XRE_main;
+XRE_DisableWritePoisoningType XRE_DisableWritePoisoning;
 
 static const nsDynamicFunctionLoad kXULFuncs[] = {
     { "XRE_GetFileFromPath", (NSFuncPtr*) &XRE_GetFileFromPath },
@@ -122,6 +123,7 @@ static const nsDynamicFunctionLoad kXULFuncs[] = {
     { "XRE_TelemetryAccumulate", (NSFuncPtr*) &XRE_TelemetryAccumulate },
     { "XRE_StartupTimelineRecord", (NSFuncPtr*) &XRE_StartupTimelineRecord },
     { "XRE_main", (NSFuncPtr*) &XRE_main },
+    { "XRE_DisableWritePoisoning", (NSFuncPtr*) &XRE_DisableWritePoisoning },
     { nullptr, nullptr }
 };
 
@@ -387,5 +389,19 @@ int main(int argc, char* argv[])
   }
 
   XPCOMGlueShutdown();
+
+
+#ifdef XP_MACOSX
+  // Allow writes again. While we would like to catch writes from static
+  // destructors to allow early exits to use _exit, we know that there is
+  // at least one such write that we don't control (see bug 826029). For
+  // now we enable writes again and early exits will have to use exit instead
+  // of _exit.
+
+  // Currently write poisoning is only available on OS X. Since on OS X we never
+  // unload XUL, it is safe to call this function after XPCOMGlueShutdown.
+  XRE_DisableWritePoisoning();
+#endif
+
   return result;
 }

toolkit/xre/nsAppRunner.cpp

@@ -4080,6 +4080,11 @@ XRE_mainMetro(int argc, char* argv[], const nsXREAppData* aAppData)
 void SetWindowsEnvironment(WindowsEnvironmentType aEnvID);
 #endif // MOZ_METRO || !defined(XP_WIN)
 
+void
+XRE_DisableWritePoisoning(void) {
+  mozilla::DisableWritePoisoning();
+}
+
 int
 XRE_main(int argc, char* argv[], const nsXREAppData* aAppData, uint32_t aFlags)
 {

xpcom/build/nsXULAppAPI.h

@@ -452,6 +452,8 @@ XRE_API(void,
 XRE_API(void,
         XRE_InitOmnijar, (nsIFile* greOmni,
                           nsIFile* appOmni))
+XRE_API(void,
+        XRE_DisableWritePoisoning, (void))
 
 #ifdef XP_WIN
 /**