diff -up firefox-66.0/js/src/util/NativeStack.cpp.mozilla-1533969 firefox-66.0/js/src/util/NativeStack.cpp
--- firefox-66.0/js/src/util/NativeStack.cpp.mozilla-1533969	2019-03-14 23:12:13.000000000 +0100
+++ firefox-66.0/js/src/util/NativeStack.cpp	2019-03-22 15:17:08.338328211 +0100
@@ -25,7 +25,7 @@
 #    include <sys/syscall.h>
 #    include <sys/types.h>
 #    include <unistd.h>
-static pid_t gettid() { return syscall(__NR_gettid); }
+#    define gettid() static_cast<pid_t>(syscall(__NR_gettid))
 #  endif
 #else
 #  error "Unsupported platform"
diff -up firefox-66.0/tools/profiler/core/platform.h.mozilla-1533969 firefox-66.0/tools/profiler/core/platform.h
--- firefox-66.0/tools/profiler/core/platform.h.mozilla-1533969	2019-03-22 15:17:08.338328211 +0100
+++ firefox-66.0/tools/profiler/core/platform.h	2019-03-22 15:19:00.046748130 +0100
@@ -47,11 +47,11 @@
 #if defined(__GLIBC__)
 #  include <unistd.h>
 #  include <sys/syscall.h>
-static inline pid_t gettid() { return (pid_t)syscall(SYS_gettid); }
+#  define gettid() static_cast<pid_t>(syscall(SYS_gettid))
 #elif defined(GP_OS_darwin)
 #  include <unistd.h>
 #  include <sys/syscall.h>
-static inline pid_t gettid() { return (pid_t)syscall(SYS_thread_selfid); }
+#  define gettid() static_cast<pid_t>(syscall(SYS_thread_selfid))
 #elif defined(GP_OS_android)
 #  include <unistd.h>
 #elif defined(GP_OS_windows)