diff --git a/build/pure_virtual/moz.build b/build/pure_virtual/moz.build
new file mode 100644
index 000000000000..c49cb8fe80cb
--- /dev/null
+++ b/build/pure_virtual/moz.build
@@ -0,0 +1,17 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+Library("pure_virtual")
+
+SOURCES += ["pure_virtual.c"]
+
+FORCE_STATIC_LIB = True
+
+USE_STATIC_LIBS = True
+
+# Build a real library so that the linker can remove it if the symbol
+# is never used.
+NO_EXPAND_LIBS = True
diff --git a/build/pure_virtual/pure_virtual.c b/build/pure_virtual/pure_virtual.c
new file mode 100644
index 000000000000..23b18f2aae7d
--- /dev/null
+++ b/build/pure_virtual/pure_virtual.c
@@ -0,0 +1,27 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <mozilla/Assertions.h>
+
+// This function is used in vtables to point at pure virtual methods.
+// The implementation in the standard library usually aborts, but
+// the function is normally never called (a call would be a bug).
+// Each of these entries in vtables, however, require an unnecessary
+// dynamic relocation. Defining our own function makes the linker
+// point the vtables here instead of the standard library, replacing
+// the dynamic relocations with relative relocations.
+//
+// On Windows, it doesn't really make a difference, but on macOS it
+// can be packed better, saving about 10KB in libxul, and on 64-bits
+// ELF systems, with packed relative relocations, it saves 140KB.
+//
+// Another advantage of having our own is that we can use MOZ_CRASH
+// instead of the system's abort.
+#ifdef _MSC_VER
+int __cdecl _purecall() { MOZ_CRASH("pure virtual call"); }
+#else
+__attribute__((visibility("hidden"))) void __cxa_pure_virtual() {
+  MOZ_CRASH("pure virtual call");
+}
+#endif
diff --git a/mfbt/moz.build b/mfbt/moz.build
index 4cdcfcd0fc3d..5f8c0925a545 100644
--- a/mfbt/moz.build
+++ b/mfbt/moz.build
@@ -205,3 +205,8 @@ if CONFIG["MOZ_NEEDS_LIBATOMIC"]:
     OS_LIBS += ["atomic"]
 
 DEFINES["LZ4LIB_VISIBILITY"] = ""
+
+# This is kind of gross because this is not a subdirectory,
+# but pure_virtual requires mfbt to build and some projects
+# don't use mfbt.
+DIRS += ["../build/pure_virtual"]
diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index 360205f8ec97..f4100772418e 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -388,6 +388,8 @@ class TreeMetadataEmitter(LoggingMixin):
                     context, obj, variable, self.STDCXXCOMPAT_NAME[obj.KIND]
                 )
             if obj.KIND == "target":
+                if "pure_virtual" in self._libs:
+                    self._link_library(context, obj, variable, "pure_virtual")
                 for lib in context.config.substs.get("STLPORT_LIBS", []):
                     obj.link_system_library(lib)
 
diff --git a/toolkit/crashreporter/test/unit/test_crash_purevirtual.js b/toolkit/crashreporter/test/unit/test_crash_purevirtual.js
index e482eaa41586..cc81c008df09 100644
--- a/toolkit/crashreporter/test/unit/test_crash_purevirtual.js
+++ b/toolkit/crashreporter/test/unit/test_crash_purevirtual.js
@@ -6,14 +6,6 @@ add_task(async function run_test() {
     return;
   }
 
-  var isOSX = "nsILocalFileMac" in Ci;
-  if (isOSX) {
-    dump(
-      "INFO | test_crash_purevirtual.js | TODO: purecalls not caught on OS X\n"
-    );
-    return;
-  }
-
   // Try crashing with a pure virtual call
   await do_crash(
     function () {