diff -up firefox-64.0/build/moz.configure/toolchain.configure.1516081 firefox-64.0/build/moz.configure/toolchain.configure
--- firefox-64.0/build/moz.configure/toolchain.configure.1516081	2018-12-07 03:56:20.000000000 +0100
+++ firefox-64.0/build/moz.configure/toolchain.configure	2019-01-03 15:30:08.207368056 +0100
@@ -1304,7 +1304,7 @@ def pgo_flags(compiler, build_env, targe
 
     if compiler.type == 'gcc':
         return namespace(
-            gen_cflags=['-fprofile-generate'],
+            gen_cflags=['-fprofile-generate', '-DMOZ_PROFILE_INSTRUMENTATION'],
             gen_ldflags=['-fprofile-generate'],
             use_cflags=['-fprofile-use', '-fprofile-correction',
                         '-Wcoverage-mismatch'],
@@ -1325,7 +1325,8 @@ def pgo_flags(compiler, build_env, targe
 
         if gen_ldflags:
             return namespace(
-                gen_cflags=['-fprofile-instr-generate'],
+                gen_cflags=['-fprofile-instr-generate',
+			    '-DMOZ_PROFILE_INSTRUMENTATION'],
                 gen_ldflags=gen_ldflags,
                 use_cflags=['-fprofile-instr-use=%s' % profdata,
                             '-Wno-error=profile-instr-out-of-date',
diff -up firefox-64.0/toolkit/components/terminator/nsTerminator.cpp.1516081 firefox-64.0/toolkit/components/terminator/nsTerminator.cpp
--- firefox-64.0/toolkit/components/terminator/nsTerminator.cpp.1516081	2019-01-03 15:30:08.207368056 +0100
+++ firefox-64.0/toolkit/components/terminator/nsTerminator.cpp	2019-01-03 15:31:33.445034029 +0100
@@ -419,6 +419,12 @@
     }
   }
 #endif
+  // Disable watchdog for PGO train builds - writting profile information at
+  // exit may take time and it is better to make build hang rather than
+  // silently produce poorly performing binary.
+#ifdef MOZ_PROFILE_INSTRUMENTATION
+  crashAfterMS = INT32_MAX;
+#endif
 
   UniquePtr<Options> options(new Options());
   const PRIntervalTime ticksDuration = PR_MillisecondsToInterval(1000);