--- a/dom/base/nsFrameMessageManager.cpp
+++ b/dom/base/nsFrameMessageManager.cpp
@@ -1647,17 +1647,17 @@ nsMessageManagerScriptExecutor::TryCache
 
     JS::SourceBufferHolder srcBuf(dataStringBuf, dataStringLength,
                                   JS::SourceBufferHolder::GiveOwnership);
 
     if (!dataStringBuf || dataStringLength == 0) {
       return;
     }
 
-    JS::CompileOptions options(cx, JSVERSION_LATEST);
+    JS::CompileOptions options(cx, JSVERSION_DEFAULT);
     options.setFileAndLine(url.get(), 1);
     options.setNoScriptRval(true);
 
     if (aRunInGlobalScope) {
       if (!JS::Compile(cx, options, srcBuf, &script)) {
         return;
       }
     // We're going to run these against some non-global scope.
@@ -1713,17 +1713,17 @@ nsMessageManagerScriptExecutor::InitChil
   AutoSafeJSContext cx;
   nsContentUtils::GetSecurityManager()->GetSystemPrincipal(getter_AddRefs(mPrincipal));
 
   nsIXPConnect* xpc = nsContentUtils::XPConnect();
   const uint32_t flags = nsIXPConnect::INIT_JS_STANDARD_CLASSES;
 
   JS::CompartmentOptions options;
   options.creationOptions().setSystemZone();
-  options.behaviors().setVersion(JSVERSION_LATEST);
+  options.behaviors().setVersion(JSVERSION_DEFAULT);
 
   if (xpc::SharedMemoryEnabled()) {
     options.creationOptions().setSharedMemoryAndAtomicsEnabled(true);
   }
 
   nsCOMPtr<nsIXPConnectJSObjectHolder> globalHolder;
   nsresult rv =
     xpc->InitClassesWithNewWrappedGlobal(cx, aScope, mPrincipal,

--- a/dom/security/test/cors/browser_CORS-console-warnings.js
+++ b/dom/security/test/cors/browser_CORS-console-warnings.js
@@ -22,17 +22,17 @@ function on_new_message(event, new_messa
     let text = elem.textContent;
     if (text.match('Cross-Origin Request Blocked:')) {
       ok(true, "message is: " + text);
       messages_seen++;
     }
   }
 }
 
-function do_cleanup() {
+function* do_cleanup() {
   if (webconsole) {
     webconsole.ui.off("new-messages", on_new_message);
   }
   yield unsetCookiePref();
 }
 
 /**
  * Set e10s related preferences in the test environment.

--- a/dom/workers/RuntimeService.cpp
+++ b/dom/workers/RuntimeService.cpp
@@ -2015,17 +2015,17 @@ RuntimeService::Init()
       MOZ_CRASH("Unable to connect PBackground actor for the main thread!");
     }
   }
 
   // Initialize JSSettings.
   if (!sDefaultJSSettings.gcSettings[0].IsSet()) {
     sDefaultJSSettings.contextOptions = JS::ContextOptions();
     sDefaultJSSettings.chrome.maxScriptRuntime = -1;
-    sDefaultJSSettings.chrome.compartmentOptions.behaviors().setVersion(JSVERSION_LATEST);
+    sDefaultJSSettings.chrome.compartmentOptions.behaviors().setVersion(JSVERSION_DEFAULT);
     sDefaultJSSettings.content.maxScriptRuntime = MAX_SCRIPT_RUN_TIME_SEC;
 #ifdef JS_GC_ZEAL
     sDefaultJSSettings.gcZealFrequency = JS_DEFAULT_ZEAL_FREQ;
     sDefaultJSSettings.gcZeal = 0;
 #endif
     SetDefaultJSGCSettings(JSGC_MAX_BYTES, WORKER_DEFAULT_RUNTIME_HEAPSIZE);
     SetDefaultJSGCSettings(JSGC_ALLOCATION_THRESHOLD,
                            WORKER_DEFAULT_ALLOCATION_THRESHOLD);

--- a/dom/workers/ScriptLoader.cpp
+++ b/dom/workers/ScriptLoader.cpp
@@ -1956,17 +1956,17 @@ ScriptExecutorRunnable::WorkerRun(JSCont
 
     NS_ConvertUTF16toUTF8 filename(loadInfo.mURL);
 
     JS::CompileOptions options(aCx);
     options.setFileAndLine(filename.get(), 1)
            .setNoScriptRval(true);
 
     if (mScriptLoader.mWorkerScriptType == DebuggerScript) {
-      options.setVersion(JSVERSION_LATEST);
+      options.setVersion(JSVERSION_DEFAULT);
     }
 
     MOZ_ASSERT(loadInfo.mMutedErrorFlag.isSome());
     options.setMutedErrors(loadInfo.mMutedErrorFlag.valueOr(true));
 
     JS::SourceBufferHolder srcBuf(loadInfo.mScriptTextBuf,
                                   loadInfo.mScriptTextLength,
                                   JS::SourceBufferHolder::GiveOwnership);

--- a/dom/xbl/nsXBLProtoImplField.cpp
+++ b/dom/xbl/nsXBLProtoImplField.cpp
@@ -429,17 +429,17 @@ nsXBLProtoImplField::InstallField(JS::Ha
   NS_ENSURE_TRUE(scopeObject, NS_ERROR_OUT_OF_MEMORY);
 
   AutoEntryScript aes(scopeObject, "XBL <field> initialization", true);
   JSContext* cx = aes.cx();
 
   JS::Rooted<JS::Value> result(cx);
   JS::CompileOptions options(cx);
   options.setFileAndLine(uriSpec.get(), mLineNumber)
-         .setVersion(JSVERSION_LATEST);
+         .setVersion(JSVERSION_DEFAULT);
   JS::AutoObjectVector scopeChain(cx);
   if (!nsJSUtils::GetScopeChainForElement(cx, boundElement, scopeChain)) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
   rv = NS_OK;
   {
     nsJSUtils::ExecutionContext exec(cx, scopeObject);
     exec.SetScopeChain(scopeChain);

--- a/dom/xbl/nsXBLProtoImplMethod.cpp
+++ b/dom/xbl/nsXBLProtoImplMethod.cpp
@@ -188,17 +188,17 @@ nsXBLProtoImplMethod::CompileMember(Auto
     functionUri.Truncate(hash);
   }
 
   JSContext *cx = jsapi.cx();
   JSAutoCompartment ac(cx, aClassObject);
   JS::CompileOptions options(cx);
   options.setFileAndLine(functionUri.get(),
                          uncompiledMethod->mBodyText.GetLineNumber())
-         .setVersion(JSVERSION_LATEST);
+         .setVersion(JSVERSION_DEFAULT);
   JS::Rooted<JSObject*> methodObject(cx);
   JS::AutoObjectVector emptyVector(cx);
   nsresult rv = nsJSUtils::CompileFunction(jsapi, emptyVector, options, cname,
                                            paramCount,
                                            const_cast<const char**>(args),
                                            body, methodObject.address());
 
   // Destroy our uncompiled method and delete our arg list.

--- a/dom/xbl/nsXBLProtoImplProperty.cpp
+++ b/dom/xbl/nsXBLProtoImplProperty.cpp
@@ -194,17 +194,17 @@ nsXBLProtoImplProperty::CompileMember(Au
   bool deletedGetter = false;
   nsXBLTextWithLineNumber *getterText = mGetter.GetUncompiled();
   if (getterText && getterText->GetText()) {
     nsDependentString getter(getterText->GetText());
     if (!getter.IsEmpty()) {
       JSAutoCompartment ac(cx, aClassObject);
       JS::CompileOptions options(cx);
       options.setFileAndLine(functionUri.get(), getterText->GetLineNumber())
-             .setVersion(JSVERSION_LATEST);
+             .setVersion(JSVERSION_DEFAULT);
       nsCString name = NS_LITERAL_CSTRING("get_") + NS_ConvertUTF16toUTF8(mName);
       JS::Rooted<JSObject*> getterObject(cx);
       JS::AutoObjectVector emptyVector(cx);
       rv = nsJSUtils::CompileFunction(jsapi, emptyVector, options, name, 0,
                                       nullptr, getter, getterObject.address());
 
       delete getterText;
       deletedGetter = true;
@@ -240,17 +240,17 @@ nsXBLProtoImplProperty::CompileMember(Au
   bool deletedSetter = false;
   nsXBLTextWithLineNumber *setterText = mSetter.GetUncompiled();
   if (setterText && setterText->GetText()) {
     nsDependentString setter(setterText->GetText());
     if (!setter.IsEmpty()) {
       JSAutoCompartment ac(cx, aClassObject);
       JS::CompileOptions options(cx);
       options.setFileAndLine(functionUri.get(), setterText->GetLineNumber())
-             .setVersion(JSVERSION_LATEST);
+             .setVersion(JSVERSION_DEFAULT);
       nsCString name = NS_LITERAL_CSTRING("set_") + NS_ConvertUTF16toUTF8(mName);
       JS::Rooted<JSObject*> setterObject(cx);
       JS::AutoObjectVector emptyVector(cx);
       rv = nsJSUtils::CompileFunction(jsapi, emptyVector, options, name, 1,
                                       gPropertyArgs, setter,
                                       setterObject.address());
 
       delete setterText;

--- a/dom/xbl/nsXBLPrototypeHandler.cpp
+++ b/dom/xbl/nsXBLPrototypeHandler.cpp
@@ -430,17 +430,17 @@ nsXBLPrototypeHandler::EnsureEventHandle
   const char **argNames;
   nsContentUtils::GetEventArgNames(kNameSpaceID_XBL, aName, false, &argCount,
                                    &argNames);
 
   // Compile the event handler in the xbl scope.
   JSAutoCompartment ac(cx, scopeObject);
   JS::CompileOptions options(cx);
   options.setFileAndLine(bindingURI.get(), mLineNumber)
-         .setVersion(JSVERSION_LATEST);
+         .setVersion(JSVERSION_DEFAULT);
 
   JS::Rooted<JSObject*> handlerFun(cx);
   JS::AutoObjectVector emptyVector(cx);
   rv = nsJSUtils::CompileFunction(jsapi, emptyVector, options,
                                   nsAtomCString(aName), argCount,
                                   argNames, handlerText,
                                   handlerFun.address());
   NS_ENSURE_SUCCESS(rv, rv);

--- a/dom/xul/nsXULContentSink.cpp
+++ b/dom/xul/nsXULContentSink.cpp
@@ -830,17 +830,17 @@ XULContentSinkImpl::OpenTag(const char16
     return NS_OK;
 }
 
 nsresult
 XULContentSinkImpl::OpenScript(const char16_t** aAttributes,
                                const uint32_t aLineNumber)
 {
   bool isJavaScript = true;
-  uint32_t version = JSVERSION_LATEST;
+  uint32_t version = JSVERSION_DEFAULT;
   nsresult rv;
 
   // Look for SRC attribute and look for a LANGUAGE attribute
   nsAutoString src;
   while (*aAttributes) {
       const nsDependentString key(aAttributes[0]);
       if (key.EqualsLiteral("src")) {
           src.Assign(aAttributes[1]);
@@ -856,24 +856,24 @@ XULContentSinkImpl::OpenScript(const cha
                   return NS_OK;
               }
               // We do want the warning here
               NS_ENSURE_SUCCESS(rv, rv);
           }
 
           if (nsContentUtils::IsJavascriptMIMEType(mimeType)) {
               isJavaScript = true;
-              version = JSVERSION_LATEST;
+              version = JSVERSION_DEFAULT;
 
               // Get the version string, and ensure that JavaScript supports it.
               nsAutoString versionName;
               rv = parser.GetParameter("version", versionName);
 
               if (NS_SUCCEEDED(rv)) {
-                  version = nsContentUtils::ParseJavascriptVersion(versionName);
+                  version = JSVERSION_UNKNOWN;
               } else if (rv != NS_ERROR_INVALID_ARG) {
                   return rv;
               }
           } else {
               isJavaScript = false;
           }
       } else if (key.EqualsLiteral("language")) {
           // Language is deprecated, and the impl in ScriptLoader ignores the