--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -2363,19 +2363,17 @@ nsContentUtils::IsSystemCaller(JSContext
 {
   // Note that SubjectPrincipal() assumes we are in a compartment here.
   return SubjectPrincipal(aCx) == sSystemPrincipal;
 }
 
 bool
 nsContentUtils::ThreadsafeIsSystemCaller(JSContext* aCx)
 {
-  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::Get();
-  MOZ_ASSERT(ccjscx->Context() == aCx);
-
+  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::GetFor(aCx);
   return ccjscx->IsSystemCaller();
 }
 
 // static
 bool
 nsContentUtils::LookupBindingMember(JSContext* aCx, nsIContent *aContent,
                                     JS::Handle<jsid> aId,
                                     JS::MutableHandle<JS::PropertyDescriptor> aDesc)

--- a/dom/bindings/Exceptions.cpp
+++ b/dom/bindings/Exceptions.cpp
@@ -115,17 +115,17 @@ Throw(JSContext* aCx, nsresult aRv, cons
     return false;
   }
 
   if (JS_IsExceptionPending(aCx)) {
     // Don't clobber the existing exception.
     return false;
   }
 
-  CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
+  CycleCollectedJSContext* context = CycleCollectedJSContext::GetFor(aCx);
   RefPtr<Exception> existingException = context->GetPendingException();
   // Make sure to clear the pending exception now.  Either we're going to reuse
   // it (and we already grabbed it), or we plan to throw something else and this
   // pending exception is no longer relevant.
   context->SetPendingException(nullptr);
 
   // Ignore the pending exception if we have a non-default message passed in.
   if (aMessage.IsEmpty() && existingException) {