diff --git a/js/src/gc/Nursery.cpp b/js/src/gc/Nursery.cpp
index bc10b073f669..5ec8cbb56637 100644
--- a/js/src/gc/Nursery.cpp
+++ b/js/src/gc/Nursery.cpp
@@ -487,20 +487,22 @@ js::Nursery::renderProfileJSON(JSONPrinter& json) const
         // requested. (And as a public API, this function should not crash in
         // such a case.)
         json.beginObject();
-        json.property("status", "no collection");
+        json.property("status", "nursery empty");
         json.endObject();
         return;
     }
 
     json.beginObject();
 
+    json.property("status", "complete");
+
     json.property("reason", JS::gcreason::ExplainReason(previousGC.reason));
     json.property("bytes_tenured", previousGC.tenuredBytes);
-    json.floatProperty("promotion_rate", calcPromotionRate(nullptr), 0);
-    json.property("nursery_bytes", previousGC.nurseryUsedBytes);
-    json.property("new_nursery_bytes", numChunks() * ChunkSize);
+    json.property("bytes_used", previousGC.nurseryUsedBytes);
+    json.property("cur_capacity", previousGC.nurseryCapacity);
+    json.property("new_capacity", spaceToEnd());
 
-    json.beginObjectProperty("timings");
+    json.beginObjectProperty("phase_times");
 
 #define EXTRACT_NAME(name, text) #name,
     static const char* names[] = {
diff --git a/js/src/gc/Statistics.cpp b/js/src/gc/Statistics.cpp
index 1c9830138c91..85765348149b 100644
--- a/js/src/gc/Statistics.cpp
+++ b/js/src/gc/Statistics.cpp
@@ -553,6 +553,14 @@ Statistics::renderNurseryJson(JSRuntime* rt) const
 UniqueChars
 Statistics::renderJsonMessage(uint64_t timestamp, bool includeSlices) const
 {
+    /*
+     * The format of the JSON message is specified by the GCMajorMarkerPayload
+     * type in perf.html
+     * https://github.com/devtools-html/perf.html/blob/master/src/types/markers.js#L62
+     *
+     * All the properties listed here are created within the timings property
+     * of the GCMajor marker.
+     */
     if (aborted)
         return DuplicateString("{status:\"aborted\"}"); // May return nullptr
 
@@ -562,10 +570,11 @@ Statistics::renderJsonMessage(uint64_t timestamp, bool includeSlices) const
     JSONPrinter json(printer);
 
     json.beginObject();
+    json.property("status", "completed");
     formatJsonDescription(timestamp, json);
 
     if (includeSlices) {
-        json.beginListProperty("slices");
+        json.beginListProperty("slices_list");
         for (unsigned i = 0; i < slices_.length(); i++)
             formatJsonSlice(i, json);
         json.endList();
@@ -609,11 +618,13 @@ Statistics::formatJsonDescription(uint64_t timestamp, JSONPrinter& json) const
     json.property("scc_sweep_max_pause", sccLongest, JSONPrinter::MILLISECONDS);
 
     json.property("nonincremental_reason", ExplainAbortReason(nonincrementalReason_));
-    json.property("allocated", uint64_t(preBytes) / 1024 / 1024);
+    json.property("allocated", uint64_t(preBytes)/1024/1024);
+    json.property("allocated_bytes", preBytes);
     json.property("added_chunks", getCount(STAT_NEW_CHUNK));
     json.property("removed_chunks", getCount(STAT_DESTROY_CHUNK));
     json.property("major_gc_number", startingMajorGCNumber);
     json.property("minor_gc_number", startingMinorGCNumber);
+    json.property("slice_number", startingSliceNumber);
 }
 
 void
@@ -879,6 +890,7 @@ Statistics::beginGC(JSGCInvocationKind kind)
 
     preBytes = runtime->gc.usage.gcBytes();
     startingMajorGCNumber = runtime->gc.majorGCCount();
+    startingSliceNumber = runtime->gc.gcNumber();
 }
 
 void
diff --git a/js/src/gc/Statistics.h b/js/src/gc/Statistics.h
index 4ad22903be5b..f40c75ed8a21 100644
--- a/js/src/gc/Statistics.h
+++ b/js/src/gc/Statistics.h
@@ -314,6 +314,7 @@ struct Statistics
     /* GC numbers as of the beginning of the collection. */
     uint64_t startingMinorGCNumber;
     uint64_t startingMajorGCNumber;
+    uint64_t startingSliceNumber;
 
     /* Records the maximum GC pause in an API-controlled interval (in us). */
     mutable TimeDuration maxPauseInInterval;
diff --git a/tools/profiler/core/platform.cpp b/tools/profiler/core/platform.cpp
index 0fb894382fe4..e3c297f8d882 100755
--- a/tools/profiler/core/platform.cpp
+++ b/tools/profiler/core/platform.cpp
@@ -1447,7 +1447,7 @@ StreamMetaJSCustomObject(PSLockRef aLock, SpliceableJSONWriter& aWriter,
 {
   MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));
 
-  aWriter.IntProperty("version", 8);
+  aWriter.IntProperty("version", 9);
 
   // The "startTime" field holds the number of milliseconds since midnight
   // January 1, 1970 GMT. This grotty code computes (Now - (Now -