diff -up firefox-71.0/build/moz.configure/lto-pgo.configure.1516081 firefox-71.0/build/moz.configure/lto-pgo.configure
--- firefox-71.0/build/moz.configure/lto-pgo.configure.1516081	2019-11-26 01:02:19.000000000 +0100
+++ firefox-71.0/build/moz.configure/lto-pgo.configure	2019-11-26 11:04:10.993077232 +0100
@@ -71,7 +71,7 @@ set_config('PGO_PROFILE_PATH', pgo_profi
 def pgo_flags(compiler, target, profdata):
     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'],
@@ -92,7 +92,7 @@ def pgo_flags(compiler, target, profdata
             gen_ldflags = ['-fprofile-generate']
 
         return namespace(
-            gen_cflags=[prefix + '-fprofile-generate'],
+            gen_cflags=[prefix + '-fprofile-generate', '-DMOZ_PROFILE_INSTRUMENTATION'],
             gen_ldflags=gen_ldflags,
             use_cflags=[prefix + '-fprofile-use=%s' % profdata,
                         # Some error messages about mismatched profile data