diff --git a/dom/base/ScriptSettings.cpp b/dom/base/ScriptSettings.cpp
index c085f3ae74d0..82e51101dc87 100644
--- a/dom/base/ScriptSettings.cpp
+++ b/dom/base/ScriptSettings.cpp
@@ -312,7 +312,6 @@ AutoJSAPI::~AutoJSAPI()
 {
   if (mOwnErrorReporting) {
     MOZ_ASSERT(NS_IsMainThread(), "See corresponding assertion in TakeOwnershipOfErrorReporting()");
-    JS::ContextOptionsRef(cx()).setAutoJSAPIOwnsErrorReporting(mOldAutoJSAPIOwnsErrorReporting);
 
     if (HasException()) {
 
@@ -342,6 +341,13 @@ AutoJSAPI::~AutoJSAPI()
         NS_WARNING("OOMed while acquiring uncaught exception from JSAPI");
       }
     }
+
+    // We need to do this _after_ processing the existing exception, because the
+    // JS engine can throw while doing that, and uses this bit to determine what
+    // to do in that case: squelch the exception if the bit is set, otherwise
+    // call the error reporter. Calling WarningOnlyErrorReporter with a
+    // non-warning will assert, so we need to make sure we do the former.
+    JS::ContextOptionsRef(cx()).setAutoJSAPIOwnsErrorReporting(mOldAutoJSAPIOwnsErrorReporting);
   }
 
   if (mOldErrorReporter.isSome()) {
diff --git a/js/src/jscntxt.cpp b/js/src/jscntxt.cpp
index 44222f47a992..6d91de1c7b3e 100644
--- a/js/src/jscntxt.cpp
+++ b/js/src/jscntxt.cpp
@@ -229,6 +229,13 @@ ReportError(JSContext *cx, const char *message, JSErrorReport *reportp,
     if (cx->options().autoJSAPIOwnsErrorReporting() || JS_IsRunning(cx)) {
         if (ErrorToException(cx, message, reportp, callback, userRef))
             return;
+
+        /*
+         * The AutoJSAPI error reporter only allows warnings to be reported so
+         * just ignore this error rather than try to report it.
+         */
+        if (cx->options().autoJSAPIOwnsErrorReporting())
+            return;
     }
 
     /*
diff --git a/js/src/jsexn.cpp b/js/src/jsexn.cpp
index ce9f2c44e278..e9abba006ced 100644
--- a/js/src/jsexn.cpp
+++ b/js/src/jsexn.cpp
@@ -608,6 +608,12 @@ js::ErrorToException(JSContext *cx, const char *message, JSErrorReport *reportp,
 static bool
 IsDuckTypedErrorObject(JSContext *cx, HandleObject exnObject, const char **filename_strp)
 {
+    /*
+     * This function is called from ErrorReport::init and so should not generate
+     * any new exceptions.
+     */
+    AutoClearPendingException acpe(cx);
+
     bool found;
     if (!JS_HasProperty(cx, exnObject, js_message_str, &found) || !found)
         return false;
diff --git a/js/src/jsexn.h b/js/src/jsexn.h
index f601c03cca6c..5a5f6f3c3bcd 100644
--- a/js/src/jsexn.h
+++ b/js/src/jsexn.h
@@ -115,6 +115,20 @@ ExnTypeFromProtoKey(JSProtoKey key)
     return type;
 }
 
+class AutoClearPendingException
+{
+    JSContext *cx;
+
+  public:
+    explicit AutoClearPendingException(JSContext *cxArg)
+      : cx(cxArg)
+    { }
+
+    ~AutoClearPendingException() {
+        cx->clearPendingException();
+    }
+};
+
 } // namespace js
 
 #endif /* jsexn_h */