--- a/mfbt/WeakPtr.h
+++ b/mfbt/WeakPtr.h
@@ -83,18 +83,29 @@
 // the real object destruction just between when thread A is storing
 // the object pointer locally and is about to add a reference to it.
 //
 // Hence, a non-null weak proxy object is considered to have a single
 // "owning thread".  It means that each query for a weak reference,
 // its dereference, and destruction of the real object must all happen
 // on a single thread.  The following macros implement assertions for
 // checking these conditions.
+//
+// We disable this on MinGW. MinGW has two threading models: win32
+// API based, which disables std::thread; and POSIX based which
+// enables it but requires an emulation library (winpthreads).
+// Rather than attempting to switch to pthread emulation at this point,
+// we are disabling the std::thread based assertion checking.
+//
+// In the future, to enable it we could
+// a. have libgcc/stdc++ support win32 threads natively
+// b. switch to POSIX-based threading in MinGW with pthread emulation
+// c. refactor it to not use std::thread
 
-#if defined(DEBUG) || (defined(NIGHTLY_BUILD) && !defined(MOZ_PROFILING))
+#if !defined(__MINGW32__) && (defined(DEBUG) || (defined(NIGHTLY_BUILD) && !defined(MOZ_PROFILING)))
 
 #include <thread>
 #define MOZ_WEAKPTR_DECLARE_THREAD_SAFETY_CHECK \
   std::thread::id _owningThread; \
   bool _empty; // If it was initialized as a placeholder with mPtr = nullptr.
 #define MOZ_WEAKPTR_INIT_THREAD_SAFETY_CHECK() \
   do { \
     _owningThread = std::this_thread::get_id(); \