diff --git a/pythonlib/camoufox/utils.py b/pythonlib/camoufox/utils.py
index 7282856..2f75d95 100644
--- a/pythonlib/camoufox/utils.py
+++ b/pythonlib/camoufox/utils.py
@@ -6,7 +6,7 @@ from os.path import abspath
 from pathlib import Path
 from pprint import pprint
 from random import randint, randrange
-from typing import Any, Dict, List, Literal, Optional, Tuple, Union, cast
+from typing import Any, Dict, List, Literal, Optional, Tuple, Union
 
 import numpy as np
 import orjson
@@ -601,8 +601,10 @@ def launch_options(
         custom_fonts_only = False
     if i_know_what_im_doing is None:
         i_know_what_im_doing = False
-    if env is None:
-        env = cast(Dict[str, Union[str, float, bool]], environ)
+    # Keep per-launch overrides isolated from the process environment and from
+    # mappings supplied by callers. In particular, DISPLAY must not outlive the
+    # virtual display that owns it.
+    env = dict(environ) if env is None else dict(env)
     if isinstance(executable_path, str):
         # Convert executable path to a Path object
         executable_path = Path(abspath(executable_path))
diff --git a/pythonlib/tests/test_launch_environment.py b/pythonlib/tests/test_launch_environment.py
new file mode 100644
index 0000000..b462528
--- /dev/null
+++ b/pythonlib/tests/test_launch_environment.py
@@ -0,0 +1,76 @@
+"""Regression tests for per-launch environment isolation."""
+
+import os
+
+import pytest
+
+from camoufox import utils
+
+
+@pytest.fixture
+def isolated_launch_dependencies(monkeypatch):
+    """Keep launch_options focused on environment assembly, without a browser."""
+    monkeypatch.setattr(utils, "add_default_addons", lambda *args, **kwargs: None)
+    monkeypatch.setattr(utils, "generate_fingerprint", lambda *args, **kwargs: object())
+    monkeypatch.setattr(utils, "from_browserforge", lambda *args, **kwargs: {})
+    monkeypatch.setattr(utils, "get_screen_cons", lambda *args, **kwargs: None)
+    monkeypatch.setattr(utils, "_generate_random_font_subset", lambda *args: [])
+    monkeypatch.setattr(utils, "_generate_random_voice_subset", lambda *args: [])
+    monkeypatch.setattr(utils, "fix_navigator_arch", lambda *args: None)
+    monkeypatch.setattr(utils, "fix_screen_no_taskbar", lambda *args: None)
+    monkeypatch.setattr(utils, "clamp_window_dimensions", lambda *args: None)
+    monkeypatch.setattr(utils, "set_media_devices_defaults", lambda *args: None)
+    monkeypatch.setattr(utils, "installed_verstr", lambda: "152.0.4-beta.28")
+    monkeypatch.setattr(utils, "validate_config", lambda *args, **kwargs: None)
+    monkeypatch.setattr(utils, "get_env_vars", lambda *args, **kwargs: {})
+    monkeypatch.setattr(utils, "launch_path", lambda: "/test/camoufox")
+
+
+def _launch_with_virtual_display(**kwargs):
+    return utils.launch_options(
+        virtual_display=":4242",
+        headless=True,
+        block_webgl=True,
+        i_know_what_im_doing=True,
+        **kwargs,
+    )
+
+
+def test_virtual_display_does_not_mutate_process_environment(
+    monkeypatch, isolated_launch_dependencies
+):
+    monkeypatch.delenv("DISPLAY", raising=False)
+    monkeypatch.setenv("GDK_BACKEND", "wayland")
+    monkeypatch.setenv("WAYLAND_DISPLAY", "wayland-0")
+    monkeypatch.setenv("MOZ_ENABLE_WAYLAND", "1")
+    keys = ("DISPLAY", "GDK_BACKEND", "WAYLAND_DISPLAY", "MOZ_ENABLE_WAYLAND")
+    before = {key: os.environ.get(key) for key in keys}
+
+    options = _launch_with_virtual_display()
+
+    assert {key: os.environ.get(key) for key in keys} == before
+    assert options["env"]["DISPLAY"] == ":4242"
+    assert options["env"]["GDK_BACKEND"] == "x11"
+    assert "WAYLAND_DISPLAY" not in options["env"]
+    assert options["env"]["MOZ_ENABLE_WAYLAND"] == "0"
+
+
+def test_virtual_display_does_not_mutate_caller_environment(
+    isolated_launch_dependencies,
+):
+    caller_env = {
+        "UNCHANGED": "value",
+        "GDK_BACKEND": "wayland",
+        "WAYLAND_DISPLAY": "wayland-0",
+        "MOZ_ENABLE_WAYLAND": "1",
+    }
+    before = caller_env.copy()
+
+    options = _launch_with_virtual_display(env=caller_env)
+
+    assert caller_env == before
+    assert options["env"]["UNCHANGED"] == "value"
+    assert options["env"]["DISPLAY"] == ":4242"
+    assert options["env"]["GDK_BACKEND"] == "x11"
+    assert "WAYLAND_DISPLAY" not in options["env"]
+    assert options["env"]["MOZ_ENABLE_WAYLAND"] == "0"