--- a/xpcom/threads/nsMemoryPressure.cpp
+++ b/xpcom/threads/nsMemoryPressure.cpp
@@ -22,30 +22,31 @@ NS_GetPendingMemoryPressure()
   int32_t value = sMemoryPressurePending.exchange(MemPressure_None);
   return MemoryPressureState(value);
 }
 
 void
 NS_DispatchEventualMemoryPressure(MemoryPressureState aState)
 {
   /*
-   * A new memory pressure event erases an ongoing memory pressure, but an
-   * existing "new" memory pressure event takes precedence over a new "ongoing"
-   * memory pressure event.
+   * A new memory pressure event erases an ongoing (or stop of) memory pressure,
+   * but an existing "new" memory pressure event takes precedence over a new
+   * "ongoing" or "stop" memory pressure event.
    */
   switch (aState) {
     case MemPressure_None:
       sMemoryPressurePending = MemPressure_None;
       break;
     case MemPressure_New:
       sMemoryPressurePending = MemPressure_New;
       break;
     case MemPressure_Ongoing:
+    case MemPressure_Stopping:
       sMemoryPressurePending.compareExchange(MemPressure_None,
-                                             MemPressure_Ongoing);
+                                             aState);
       break;
   }
 }
 
 nsresult
 NS_DispatchMemoryPressure(MemoryPressureState aState)
 {
   NS_DispatchEventualMemoryPressure(aState);

--- a/xpcom/threads/nsMemoryPressure.h
+++ b/xpcom/threads/nsMemoryPressure.h
@@ -35,17 +35,28 @@ enum MemoryPressureState
    *
    * In case of conflict with an new memory pressue, the new memory pressure
    * takes precedence over an ongoing memory pressure.  The reason being
    * that if no events are processed between 2 notifications (new followed
    * by ongoing, or ongoing followed by a new) we want to be as aggresive as
    * possible on the clean-up of the memory.  After all, we are trying to
    * keep Gecko alive as long as possible.
    */
-  MemPressure_Ongoing
+  MemPressure_Ongoing,
+
+  /*
+   * Memory pressure stopped.
+   *
+   * We're no longer under acute memory pressure, so we might want to have a
+   * chance of (cautiously) re-enabling some things we previously turned off.
+   * As above, an already enqueued new memory pressure event takes precedence.
+   * The priority ordering between concurrent attempts to queue both stopped
+   * and ongoing memory pressure is currently not defined.
+   */
+  MemPressure_Stopping
 };
 
 /**
  * Return and erase the latest state of the memory pressure event set by any of
  * the corresponding dispatch function.
  */
 MemoryPressureState
 NS_GetPendingMemoryPressure();

--- a/xpcom/threads/nsThread.cpp
+++ b/xpcom/threads/nsThread.cpp
@@ -1263,21 +1263,25 @@ nsThread::DoMainThreadSpecificProcessing
 
   // Fire a memory pressure notification, if one is pending.
   if (!ShuttingDown()) {
     MemoryPressureState mpPending = NS_GetPendingMemoryPressure();
     if (mpPending != MemPressure_None) {
       nsCOMPtr<nsIObserverService> os = services::GetObserverService();
 
       if (os) {
-        // Use no-forward to prevent the notifications from being transferred to
-        // the children of this process.
-        os->NotifyObservers(nullptr, "memory-pressure",
-                            mpPending == MemPressure_New ? u"low-memory-no-forward" :
-                            u"low-memory-ongoing-no-forward");
+        if (mpPending == MemPressure_Stopping) {
+          os->NotifyObservers(nullptr, "memory-pressure-stop", nullptr);
+        } else {
+          // Use no-forward to prevent the notifications from being transferred to
+          // the children of this process.
+          os->NotifyObservers(nullptr, "memory-pressure",
+                              mpPending == MemPressure_New ? u"low-memory-no-forward" :
+                              u"low-memory-ongoing-no-forward");
+        }
       } else {
         NS_WARNING("Can't get observer service!");
       }
     }
   }
 
   if (!ShuttingDown()) {
     SaveMemoryReportNearOOM(ShouldSaveMemoryReport::kMaybeReport);