diff --git a/pkgs/applications/networking/browsers/firefox/common.nix b/pkgs/applications/networking/browsers/firefox/common.nix
index 5fda096ee1d..25eb34c95e8 100644
--- a/pkgs/applications/networking/browsers/firefox/common.nix
+++ b/pkgs/applications/networking/browsers/firefox/common.nix
@@ -238,13 +238,17 @@ buildStdenv.mkDerivation ({
     # Set consistent remoting name to ensure wmclass matches with desktop file
     export MOZ_APP_REMOTINGNAME="${binaryName}"
 
-    # Use our own python
-    export MACH_USE_SYSTEM_PYTHON=1
-
     # AS=as in the environment causes build failure
     # https://bugzilla.mozilla.org/show_bug.cgi?id=1497286
     unset AS
 
+  '' + lib.optionalString (lib.versionAtLeast version "100.0") ''
+    # Use our own python
+    export MACH_BUILD_PYTHON_NATIVE_PACKAGE_SOURCE=system
+  '' + lib.optionalString (lib.versionOlder version "100.0") ''
+    # Use our own python
+    export MACH_USE_SYSTEM_PYTHON=1
+
   '' + lib.optionalString (lib.versionAtLeast version "95.0") ''
     # RBox WASM Sandboxing
     export WASM_CC=${pkgsCross.wasi32.stdenv.cc}/bin/${pkgsCross.wasi32.stdenv.cc.targetPrefix}cc