--- a/js/public/GCAPI.h
+++ b/js/public/GCAPI.h
@@ -40,29 +40,30 @@ typedef enum JSGCInvocationKind {
     GC_SHRINK = 1
 } JSGCInvocationKind;
 
 namespace JS {
 
 #define GCREASONS(D)                            \
     /* Reasons internal to the JS engine */     \
     D(API)                                      \
-    D(MAYBEGC)                                  \
+    D(EAGER_ALLOC_TRIGGER)                      \
     D(DESTROY_RUNTIME)                          \
     D(DESTROY_CONTEXT)                          \
     D(LAST_DITCH)                               \
     D(TOO_MUCH_MALLOC)                          \
     D(ALLOC_TRIGGER)                            \
     D(DEBUG_GC)                                 \
     D(COMPARTMENT_REVIVED)                      \
     D(RESET)                                    \
     D(OUT_OF_NURSERY)                           \
     D(EVICT_NURSERY)                            \
     D(FULL_STORE_BUFFER)                        \
     D(SHARED_MEMORY_LIMIT)                      \
+    D(PERIODIC_FULL_GC)                         \
                                                 \
     /* These are reserved for future use. */    \
     D(RESERVED0)                                \
     D(RESERVED1)                                \
     D(RESERVED2)                                \
     D(RESERVED3)                                \
     D(RESERVED4)                                \
     D(RESERVED5)                                \
@@ -73,17 +74,16 @@ namespace JS {
     D(RESERVED10)                               \
     D(RESERVED11)                               \
     D(RESERVED12)                               \
     D(RESERVED13)                               \
     D(RESERVED14)                               \
     D(RESERVED15)                               \
     D(RESERVED16)                               \
     D(RESERVED17)                               \
-    D(RESERVED18)                               \
                                                 \
     /* Reasons from Firefox */                  \
     D(DOM_WINDOW_UTILS)                         \
     D(COMPONENT_UTILS)                          \
     D(MEM_PRESSURE)                             \
     D(CC_WAITING)                               \
     D(CC_FORCED)                                \
     D(LOAD_END)                                 \

--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -3203,31 +3203,31 @@ GCRuntime::triggerZoneGC(Zone *zone, JS:
 bool
 GCRuntime::maybeGC(Zone *zone)
 {
     MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));
 
 #ifdef JS_GC_ZEAL
     if (zealMode == ZealAllocValue || zealMode == ZealPokeValue) {
         JS::PrepareForFullGC(rt);
-        gc(GC_NORMAL, JS::gcreason::MAYBEGC);
+        gc(GC_NORMAL, JS::gcreason::DEBUG_GC);
         return true;
     }
 #endif
 
     if (gcIfRequested())
         return true;
 
     if (zone->usage.gcBytes() > 1024 * 1024 &&
         zone->threshold.isCloseToAllocTrigger(zone->usage, schedulingState.inHighFrequencyGCMode()) &&
         !isIncrementalGCInProgress() &&
         !isBackgroundSweeping())
     {
         PrepareZoneForGC(zone);
-        startGC(GC_NORMAL, JS::gcreason::MAYBEGC);
+        startGC(GC_NORMAL, JS::gcreason::EAGER_ALLOC_TRIGGER);
         return true;
     }
 
     return false;
 }
 
 void
 GCRuntime::maybePeriodicFullGC()
@@ -3243,17 +3243,17 @@ GCRuntime::maybePeriodicFullGC()
      */
 #ifndef JS_MORE_DETERMINISTIC
     int64_t now = PRMJ_Now();
     if (nextFullGCTime && nextFullGCTime <= now && !isIncrementalGCInProgress()) {
         if (chunkAllocationSinceLastGC ||
             numArenasFreeCommitted > decommitThreshold)
         {
             JS::PrepareForFullGC(rt);
-            startGC(GC_SHRINK, JS::gcreason::MAYBEGC);
+            startGC(GC_SHRINK, JS::gcreason::PERIODIC_FULL_GC);
         } else {
             nextFullGCTime = now + GC_IDLE_FULL_SPAN;
         }
     }
 #endif
 }
 
 // Do all possible decommit immediately from the current thread without
@@ -6086,17 +6086,17 @@ static bool
 IsDeterministicGCReason(JS::gcreason::Reason reason)
 {
     if (reason > JS::gcreason::DEBUG_GC &&
         reason != JS::gcreason::CC_FORCED && reason != JS::gcreason::SHUTDOWN_CC)
     {
         return false;
     }
 
-    if (reason == JS::gcreason::MAYBEGC)
+    if (reason == JS::gcreason::EAGER_ALLOC_TRIGGER)
         return false;
 
     return true;
 }
 #endif
 
 gcstats::ZoneGCStats
 GCRuntime::scanZonesBeforeGC()