diff --git a/mfbt/Poison.cpp b/mfbt/Poison.cpp
index a253771a1353..f5d5b498658a 100644
--- a/mfbt/Poison.cpp
+++ b/mfbt/Poison.cpp
@@ -26,12 +26,6 @@
 #  endif
 #endif
 
-extern "C" {
-uintptr_t gMozillaPoisonValue;
-uintptr_t gMozillaPoisonBase;
-uintptr_t gMozillaPoisonSize;
-}
-
 // Freed memory is filled with a poison value, which we arrange to
 // form a pointer either to an always-unmapped region of the address
 // space, or to a page that has been reserved and rendered
@@ -169,12 +163,23 @@ static uintptr_t ReservePoisonArea(uintptr_t rgnsize) {
   MOZ_CRASH("no usable poison region identified");
 }
 
-void mozPoisonValueInit() {
-  gMozillaPoisonSize = GetDesiredRegionSize();
-  gMozillaPoisonBase = ReservePoisonArea(gMozillaPoisonSize);
-
-  if (gMozillaPoisonSize == 0) {  // can't happen
-    return;
+static uintptr_t GetPoisonValue(uintptr_t aBase, uintptr_t aSize) {
+  if (aSize == 0) {  // can't happen
+    return 0;
   }
-  gMozillaPoisonValue = gMozillaPoisonBase + gMozillaPoisonSize / 2 - 1;
+  return aBase + aSize / 2 - 1;
+}
+
+// Poison is used so pervasively throughout the codebase that we decided it was
+// best to actually use ordered dynamic initialization of globals (AKA static
+// constructors) for this. This way everything will have properly initialized
+// poison -- except other dynamic initialization code in libmozglue, which there
+// shouldn't be much of. (libmozglue is one of the first things loaded, and
+// specifically comes before libxul, so nearly all gecko code runs strictly
+// after this.)
+extern "C" {
+uintptr_t gMozillaPoisonSize = GetDesiredRegionSize();
+uintptr_t gMozillaPoisonBase = ReservePoisonArea(gMozillaPoisonSize);
+uintptr_t gMozillaPoisonValue =
+    GetPoisonValue(gMozillaPoisonBase, gMozillaPoisonSize);
 }
diff --git a/mfbt/Poison.h b/mfbt/Poison.h
index d184a8da2670..5b1fae1fd1f2 100644
--- a/mfbt/Poison.h
+++ b/mfbt/Poison.h
@@ -29,9 +29,8 @@ inline uintptr_t mozPoisonValue() { return gMozillaPoisonValue; }
 
 /**
  * Overwrite the memory block of aSize bytes at aPtr with the poison value.
- * aPtr MUST be aligned at a sizeof(uintptr_t) boundary.
- * Only an even number of sizeof(uintptr_t) bytes are overwritten, the last
- * few bytes (if any) is not overwritten.
+ * Only a multiple of sizeof(uintptr_t) bytes are overwritten, the last
+ * few bytes (if any) are not overwritten.
  */
 inline void mozWritePoison(void* aPtr, size_t aSize) {
   const uintptr_t POISON = mozPoisonValue();
@@ -43,12 +42,6 @@ inline void mozWritePoison(void* aPtr, size_t aSize) {
   }
 }
 
-/**
- * Initialize the poison value.
- * This should only be called once.
- */
-extern MFBT_API void mozPoisonValueInit();
-
 /* Values annotated by CrashReporter */
 extern MFBT_DATA uintptr_t gMozillaPoisonBase;
 extern MFBT_DATA uintptr_t gMozillaPoisonSize;
diff --git a/mozglue/build/TsanOptions.cpp b/mozglue/build/TsanOptions.cpp
index a581f8125291..444abdc03413 100644
--- a/mozglue/build/TsanOptions.cpp
+++ b/mozglue/build/TsanOptions.cpp
@@ -221,9 +221,6 @@ extern "C" const char* __tsan_default_suppressions() {
          // Bug 1506812
          "race:BeginBackgroundRead\n"
 
-         // Bug 1506910
-         "race:gMozillaPoisonValue\n"
-
          // Bug 1601286
          "race:setFlagBit\n"
          "race:isFatInline\n"
diff --git a/xpcom/build/XPCOMInit.cpp b/xpcom/build/XPCOMInit.cpp
index 63c89fb7ad91..9fd9fb255e41 100644
--- a/xpcom/build/XPCOMInit.cpp
+++ b/xpcom/build/XPCOMInit.cpp
@@ -259,8 +259,6 @@ NS_InitXPCOM(nsIServiceManager** aResult, nsIFile* aBinDirectory,
 
   sInitialized = true;
 
-  mozPoisonValueInit();
-
   NS_LogInit();
 
   NS_InitAtomTable();
@@ -495,7 +493,6 @@ NS_InitXPCOM(nsIServiceManager** aResult, nsIFile* aBinDirectory,
 
 EXPORT_XPCOM_API(nsresult)
 NS_InitMinimalXPCOM() {
-  mozPoisonValueInit();
   NS_SetMainThread();
   mozilla::TimeStamp::Startup();
   NS_LogInit();