--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -5005,32 +5005,16 @@ JS_RequestInterruptCallback(JSRuntime* r
 }
 
 JS_PUBLIC_API(bool)
 JS_IsRunning(JSContext* cx)
 {
     return cx->currentlyRunning();
 }
 
-JS_PUBLIC_API(bool)
-JS_SaveFrameChain(JSContext* cx)
-{
-    AssertHeapIsIdleOrIterating(cx);
-    CHECK_REQUEST(cx);
-    return cx->saveFrameChain();
-}
-
-JS_PUBLIC_API(void)
-JS_RestoreFrameChain(JSContext* cx)
-{
-    AssertHeapIsIdleOrIterating(cx);
-    CHECK_REQUEST(cx);
-    cx->restoreFrameChain();
-}
-
 JS::AutoSetAsyncStackForNewCalls::AutoSetAsyncStackForNewCalls(
   JSContext* cx, HandleObject stack, const char* asyncCause,
   JS::AutoSetAsyncStackForNewCalls::AsyncCallKind kind)
   : cx(cx),
     oldAsyncStack(cx, cx->runtime()->asyncStackForNewActivations),
     oldAsyncCause(cx->runtime()->asyncCauseForNewActivations),
     oldAsyncCallIsExplicit(cx->runtime()->asyncCallIsExplicit)
 {

--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -4569,33 +4569,16 @@ AddPromiseReactions(JSContext* cx, JS::H
 extern JS_PUBLIC_API(JSObject*)
 GetWaitForAllPromise(JSContext* cx, const JS::AutoObjectVector& promises);
 
 } // namespace JS
 
 extern JS_PUBLIC_API(bool)
 JS_IsRunning(JSContext* cx);
 
-/*
- * Saving and restoring frame chains.
- *
- * These two functions are used to set aside cx's call stack while that stack
- * is inactive. After a call to JS_SaveFrameChain, it looks as if there is no
- * code running on cx. Before calling JS_RestoreFrameChain, cx's call stack
- * must be balanced and all nested calls to JS_SaveFrameChain must have had
- * matching JS_RestoreFrameChain calls.
- *
- * JS_SaveFrameChain deals with cx not having any code running on it.
- */
-extern JS_PUBLIC_API(bool)
-JS_SaveFrameChain(JSContext* cx);
-
-extern JS_PUBLIC_API(void)
-JS_RestoreFrameChain(JSContext* cx);
-
 namespace JS {
 
 /**
  * This class can be used to store a pointer to the youngest frame of a saved
  * stack in the specified JSContext. This reference will be picked up by any new
  * calls performed until the class is destroyed, with the specified asyncCause,
  * that must not be empty.
  *

--- a/js/src/jscntxt.cpp
+++ b/js/src/jscntxt.cpp
@@ -963,17 +963,16 @@ JSContext::JSContext(JSRuntime* rt)
     unwrappedException_(this),
     options_(),
     overRecursed_(false),
     propagatingForcedReturn_(false),
     liveVolatileJitFrameIterators_(nullptr),
     reportGranularity(JS_DEFAULT_JITREPORT_GRANULARITY),
     resolvingList(nullptr),
     generatingError(false),
-    savedFrameChains_(),
     cycleDetectorSet(this),
     data(nullptr),
     data2(nullptr),
     outstandingRequests(0),
     jitIsBroken(false)
 {
     MOZ_ASSERT(static_cast<ContextFriendFields*>(this) ==
                ContextFriendFields::get(this));
@@ -1019,44 +1018,16 @@ JSContext::isThrowingDebuggeeWouldRun()
 {
     return throwing &&
            unwrappedException_.isObject() &&
            unwrappedException_.toObject().is<ErrorObject>() &&
            unwrappedException_.toObject().as<ErrorObject>().type() == JSEXN_DEBUGGEEWOULDRUN;
 }
 
 bool
-JSContext::saveFrameChain()
-{
-    if (!savedFrameChains_.append(SavedFrameChain(compartment(), enterCompartmentDepth_)))
-        return false;
-
-    if (Activation* act = runtime()->activation())
-        act->saveFrameChain();
-
-    setCompartment(nullptr);
-    enterCompartmentDepth_ = 0;
-
-    return true;
-}
-
-void
-JSContext::restoreFrameChain()
-{
-    MOZ_ASSERT(enterCompartmentDepth_ == 0); // We're about to clobber it, and it
-                                            // will be wrong forevermore.
-    SavedFrameChain sfc = savedFrameChains_.popCopy();
-    setCompartment(sfc.compartment);
-    enterCompartmentDepth_ = sfc.enterCompartmentCount;
-
-    if (Activation* act = runtime()->activation())
-        act->restoreFrameChain();
-}
-
-bool
 JSContext::currentlyRunning() const
 {
     for (ActivationIterator iter(runtime()); !iter.done(); ++iter) {
         if (iter->cx() == this)
             return true;
     }
 
     return false;

--- a/js/src/jscntxt.h
+++ b/js/src/jscntxt.h
@@ -339,31 +339,16 @@ struct JSContext : public js::ExclusiveC
   public:
     int32_t             reportGranularity;  /* see vm/Probes.h */
 
     js::AutoResolving*  resolvingList;
 
     /* True if generating an error, to prevent runaway recursion. */
     bool                generatingError;
 
-    /* See JS_SaveFrameChain/JS_RestoreFrameChain. */
-  private:
-    struct SavedFrameChain {
-        SavedFrameChain(JSCompartment* comp, unsigned count)
-          : compartment(comp), enterCompartmentCount(count) {}
-        JSCompartment* compartment;
-        unsigned enterCompartmentCount;
-    };
-    typedef js::Vector<SavedFrameChain, 1, js::SystemAllocPolicy> SaveStack;
-    SaveStack           savedFrameChains_;
-  public:
-    bool saveFrameChain();
-    void restoreFrameChain();
-
-  public:
     /* State for object and array toSource conversion. */
     js::AutoCycleDetector::Set cycleDetectorSet;
 
     /* Client opaque pointers. */
     void*               data;
     void*               data2;
 
   public:

--- a/js/src/vm/Stack-inl.h
+++ b/js/src/vm/Stack-inl.h
@@ -864,17 +864,16 @@ ActivationEntryMonitor::~ActivationEntry
     cx_->runtime()->entryMonitor = entryMonitor_;
 }
 
 Activation::Activation(JSContext* cx, Kind kind)
   : cx_(cx),
     compartment_(cx->compartment()),
     prev_(cx->runtime_->activation_),
     prevProfiling_(prev_ ? prev_->mostRecentProfiling() : nullptr),
-    savedFrameChain_(0),
     hideScriptedCallerCount_(0),
     frameCache_(cx),
     asyncStack_(cx, cx->runtime_->asyncStackForNewActivations),
     asyncCause_(cx->runtime_->asyncCauseForNewActivations),
     asyncCallIsExplicit_(cx->runtime_->asyncCallIsExplicit),
     kind_(kind)
 {
     cx->runtime_->asyncStackForNewActivations = nullptr;

--- a/js/src/vm/Stack.h
+++ b/js/src/vm/Stack.h
@@ -1206,20 +1206,16 @@ class MOZ_RAII ActivationEntryMonitor
 class Activation
 {
   protected:
     JSContext* cx_;
     JSCompartment* compartment_;
     Activation* prev_;
     Activation* prevProfiling_;
 
-    // Counter incremented by JS_SaveFrameChain on the top-most activation and
-    // decremented by JS_RestoreFrameChain.
-    size_t savedFrameChain_;
-
     // Counter incremented by JS::HideScriptedCaller and decremented by
     // JS::UnhideScriptedCaller. If > 0 for the top activation,
     // DescribeScriptedCaller will return null instead of querying that
     // activation, which should prompt the caller to consult embedding-specific
     // data structures instead.
     size_t hideScriptedCallerCount_;
 
     // The cache of SavedFrame objects we have already captured when walking
@@ -1282,27 +1278,16 @@ class Activation
         MOZ_ASSERT(isJit());
         return (jit::JitActivation*)this;
     }
     WasmActivation* asWasm() const {
         MOZ_ASSERT(isWasm());
         return (WasmActivation*)this;
     }
 
-    void saveFrameChain() {
-        savedFrameChain_++;
-    }
-    void restoreFrameChain() {
-        MOZ_ASSERT(savedFrameChain_ > 0);
-        savedFrameChain_--;
-    }
-    bool hasSavedFrameChain() const {
-        return savedFrameChain_ > 0;
-    }
-
     void hideScriptedCaller() {
         hideScriptedCallerCount_++;
     }
     void unhideScriptedCaller() {
         MOZ_ASSERT(hideScriptedCallerCount_ > 0);
         hideScriptedCallerCount_--;
     }
     bool scriptedCallerIsHidden() const {