diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 79d58d2f5ee8..ff1461c73795 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -1640,7 +1640,7 @@ JS_SetNativeStackQuota(JSContext* cx, size_t systemCodeStackSize, size_t trusted
     SetNativeStackQuotaAndLimit(cx, JS::StackForTrustedScript, trustedScriptStackSize);
     SetNativeStackQuotaAndLimit(cx, JS::StackForUntrustedScript, untrustedScriptStackSize);
 
-    if (cx->isCooperativelyScheduled())
+    if (cx->isMainThreadContext())
         cx->initJitStackLimit();
 }
 
diff --git a/js/src/threading/ProtectedData.cpp b/js/src/threading/ProtectedData.cpp
index 69ed663b609e..b5baf9347379 100644
--- a/js/src/threading/ProtectedData.cpp
+++ b/js/src/threading/ProtectedData.cpp
@@ -38,14 +38,9 @@ CheckThreadLocal::check() const
 {
     JSContext* cx = TlsContext.get();
     MOZ_ASSERT(cx);
-
-    // As for CheckZone, in a cooperatively scheduled runtime the active
-    // thread is permitted access to thread local state for other suspended
-    // threads in the same runtime.
-    if (cx->isCooperativelyScheduled())
-        MOZ_ASSERT(CurrentThreadCanAccessRuntime(cx->runtime()));
-    else
-        MOZ_ASSERT(id == ThisThread::GetId());
+    MOZ_ASSERT_IF(cx->isMainThreadContext(),
+                  CurrentThreadCanAccessRuntime(cx->runtime()));
+    MOZ_ASSERT(id == ThisThread::GetId());
 }
 
 template <AllowedHelperThread Helper>
diff --git a/js/src/vm/HelperThreads.cpp b/js/src/vm/HelperThreads.cpp
index 01fed75af133..b9dfdc8ef727 100644
--- a/js/src/vm/HelperThreads.cpp
+++ b/js/src/vm/HelperThreads.cpp
@@ -2224,7 +2224,7 @@ HelperThread::threadLoop()
     JSContext cx(nullptr, JS::ContextOptions());
     {
         AutoEnterOOMUnsafeRegion oomUnsafe;
-        if (!cx.init(ContextKind::Background))
+        if (!cx.init(ContextKind::HelperThread))
             oomUnsafe.crash("HelperThread cx.init()");
     }
     cx.setHelperThread(this);
diff --git a/js/src/vm/JSContext.cpp b/js/src/vm/JSContext.cpp
index 6e3f88dfaf29..1d9b1160db8c 100644
--- a/js/src/vm/JSContext.cpp
+++ b/js/src/vm/JSContext.cpp
@@ -100,7 +100,7 @@ bool
 JSContext::init(ContextKind kind)
 {
     // Skip most of the initialization if this thread will not be running JS.
-    if (kind == ContextKind::Cooperative) {
+    if (kind == ContextKind::MainThread) {
         if (!regexpStack.ref().init())
             return false;
 
@@ -153,7 +153,7 @@ js::NewContext(uint32_t maxBytes, uint32_t maxNurseryBytes, JSRuntime* parentRun
         return nullptr;
     }
 
-    if (!cx->init(ContextKind::Cooperative)) {
+    if (!cx->init(ContextKind::MainThread)) {
         runtime->destroyRuntime();
         js_delete(cx);
         js_delete(runtime);
@@ -1220,7 +1220,7 @@ JSContext::alreadyReportedError()
 
 JSContext::JSContext(JSRuntime* runtime, const JS::ContextOptions& options)
   : runtime_(runtime),
-    kind_(ContextKind::Background),
+    kind_(ContextKind::HelperThread),
     helperThread_(nullptr),
     options_(options),
     arenas_(nullptr),
@@ -1318,7 +1318,7 @@ JSContext::~JSContext()
 {
     // Clear the ContextKind first, so that ProtectedData checks will allow us to
     // destroy this context even if the runtime is already gone.
-    kind_ = ContextKind::Background;
+    kind_ = ContextKind::HelperThread;
 
     /* Free the stuff hanging off of cx. */
     MOZ_ASSERT(!resolvingList);
diff --git a/js/src/vm/JSContext.h b/js/src/vm/JSContext.h
index da50d3af015a..2b6870959c12 100644
--- a/js/src/vm/JSContext.h
+++ b/js/src/vm/JSContext.h
@@ -80,8 +80,11 @@ extern MOZ_THREAD_LOCAL(JSContext*) TlsContext;
 
 enum class ContextKind
 {
-    Cooperative,
-    Background
+    // Context for the main thread of a JSRuntime.
+    MainThread,
+
+    // Context for a helper thread.
+    HelperThread
 };
 
 #ifdef DEBUG
@@ -122,7 +125,7 @@ struct JSContext : public JS::RootingContext,
     // currently operating on.
     void setRuntime(JSRuntime* rt);
 
-    bool isCooperativelyScheduled() const { return kind_ == js::ContextKind::Cooperative; }
+    bool isMainThreadContext() const { return kind_ == js::ContextKind::MainThread; }
 
     inline js::gc::ArenaLists* arenas() const { return arenas_; }