diff -up firefox-78.0/xpcom/base/AvailableMemoryTracker.cpp.rhbz-1821418 firefox-78.0/xpcom/base/AvailableMemoryTracker.cpp
--- firefox-78.0/xpcom/base/AvailableMemoryTracker.cpp.rhbz-1821418	2020-06-17 04:20:44.000000000 +0200
+++ firefox-78.0/xpcom/base/AvailableMemoryTracker.cpp	2020-06-25 14:50:46.369798294 +0200
@@ -157,8 +157,12 @@ bool nsAvailableMemoryWatcher::IsVirtual
 
 /* static */
 bool nsAvailableMemoryWatcher::IsCommitSpaceLow(const MEMORYSTATUSEX& aStat) {
-  if ((kLowCommitSpaceThreshold != 0) &&
-      (aStat.ullAvailPageFile < kLowCommitSpaceThreshold)) {
+  const char* threshold = getenv("MOZ_GC_THRESHOLD");
+  if (threshold) {
+    kLowCommitSpaceThreshold = atoi(threshold);
+  }
+
+  if ((kLowCommitSpaceThreshold == 0) || (aStat.ullAvailPageFile < kLowCommitSpaceThreshold)) {
     sNumLowCommitSpaceEvents++;
     CrashReporter::AnnotateCrashReport(
         CrashReporter::Annotation::LowCommitSpaceEvents,
@@ -210,12 +214,15 @@ void nsAvailableMemoryWatcher::AdjustPol
 // polling interval accordingly.
 NS_IMETHODIMP
 nsAvailableMemoryWatcher::Notify(nsITimer* aTimer) {
+  const char* threshold = getenv("MOZ_GC_THRESHOLD");
+  bool forceLowMem = (threshold && atoi(threshold) == 0);
+
   MEMORYSTATUSEX stat;
   stat.dwLength = sizeof(stat);
   bool success = GlobalMemoryStatusEx(&stat);
 
-  if (success) {
-    bool lowMemory = IsVirtualMemoryLow(stat) || IsCommitSpaceLow(stat);
+  if (success || forceLowMemory) {
+    bool lowMemory = IsVirtualMemoryLow(stat) || IsCommitSpaceLow(stat || forceLowMem);
 
     if (lowMemory) {
       SendMemoryPressureEvent();