diff -up firefox-68.7.0/xpcom/base/AvailableMemoryTracker.cpp.rhbz-1821418 firefox-68.7.0/xpcom/base/AvailableMemoryTracker.cpp
--- firefox-68.7.0/xpcom/base/AvailableMemoryTracker.cpp.rhbz-1821418	2020-04-03 21:30:08.000000000 +0200
+++ firefox-68.7.0/xpcom/base/AvailableMemoryTracker.cpp	2020-04-23 21:15:56.015491502 +0200
@@ -147,8 +147,12 @@ 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,
@@ -206,13 +210,16 @@ 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) {
+  if (success || forceLowMem) {
     bool lowMemory = IsVirtualMemoryLow(stat) || IsCommitSpaceLow(stat) ||
-                     IsPhysicalMemoryLow(stat);
+                     IsPhysicalMemoryLow(stat) || forceLowMem;
 
     if (lowMemory) {
       SendMemoryPressureEvent();