diff --git a/.mozconfig-x86_64-pc-linux-gnu b/.mozconfig-x86_64-pc-linux-gnu
index d9d2486186f4..238cbfab2ea8 100644
--- a/.mozconfig-x86_64-pc-linux-gnu
+++ b/.mozconfig-x86_64-pc-linux-gnu
@@ -10,7 +10,7 @@ fi
 
 if test "$WFX_RELEASE" || test "$WFX_PRE_RELEASE"; then
     ac_add_options --enable-lto=full
-    ac_add_options --enable-optimize="-march=x86-64 -mfpmath=sse -mprfchw -mpopcnt -msse3 -mcx16 -msahf -mtune=skylake -O3 -w"
+    ac_add_options --enable-optimize="-march=x86-64 -mfpmath=sse -mprfchw -msse3 -mcx16 -msahf -mtune=skylake -O3 -w"
     ac_add_options --enable-release
     ac_add_options --enable-rust-simd
     ac_add_options RUSTC_OPT_LEVEL=3
diff --git a/.mozconfig-x86_64-pc-windows-msvc b/.mozconfig-x86_64-pc-windows-msvc
index 9a90ebde45a5..ff75598d2048 100644
--- a/.mozconfig-x86_64-pc-windows-msvc
+++ b/.mozconfig-x86_64-pc-windows-msvc
@@ -6,7 +6,7 @@ export WINEDEBUG=-all
 
 if test "$WFX_RELEASE" || test "$WFX_PRE_RELEASE"; then
     ac_add_options --enable-lto=cross,full
-    ac_add_options --enable-optimize="-clang:-march=x86-64 -clang:-mfpmath=sse -clang:-mprfchw -clang:-mpopcnt -clang:-msse3 -clang:-mcx16 -clang:-msahf -clang:-mtune=skylake -clang:-O3 -w"
+    ac_add_options --enable-optimize="-clang:-march=x86-64 -clang:-mfpmath=sse -clang:-mprfchw -clang:-msse3 -clang:-mcx16 -clang:-msahf -clang:-mtune=skylake -clang:-O3 -w"
     ac_add_options --enable-release
     ac_add_options --enable-rust-simd
     ac_add_options RUSTC_OPT_LEVEL=3