diff --git a/marimo/_runtime/marimo_browser.py b/marimo/_runtime/marimo_browser.py
new file mode 100644
index 00000000000..8cf2114bea9
--- /dev/null
+++ b/marimo/_runtime/marimo_browser.py
@@ -0,0 +1,91 @@
+# Copyright 2025 Marimo. All rights reserved.
+from __future__ import annotations
+
+import webbrowser
+
+from marimo._runtime.context import get_context
+from marimo._runtime.context.types import ContextNotInitializedError
+
+
+def browser_open_fallback(
+    url: str, new: int = 0, autoraise: bool = False
+) -> bool:
+    """
+    Inserts an iframe with the given URL into the output.
+
+    NB Returns false on failure.
+    """
+    import inspect
+
+    import marimo as mo
+
+    del new, autoraise  # unused
+
+    try:
+        ctx = get_context()
+    except ContextNotInitializedError:
+        return False
+
+    if ctx.execution_context is None:
+        return False
+
+    # import antigravity is a real module in python. see:
+    #    github.com/python/cpython/blob/main/Lib/antigravity.py
+    # which automatically triggers a webbrowser.open call to the relevant
+    # comic. We patch webbrowser.open due to an incompatible stub:
+    #    https://pyodide.org/en/stable/usage/wasm-constraints.html
+    # so may as well hook in to customize the easter egg. Especially since
+    # iframe constraints actually block this from loading on marimo.app.
+    #
+    # For other python lore, try:
+    #   import this
+    stack = inspect.stack()
+    if len(stack) > 3 and (
+        stack[2].filename.endswith("antigravity.py")
+        or (stack[1].filename.endswith("antigravity.py"))
+    ):
+        mo.output.append(
+            mo.image(
+                "https://marimo.app/images/antigravity.png",
+                alt=(
+                    "The image shows 2 stick figures in XKCD style. The one "
+                    'on the left says:"You\'re Flying! How?", a floating '
+                    'stick figure on the right responds "marimo!"'
+                ),
+                caption=(
+                    'Original alt text: "<i>I wrote 20 short programs in '
+                    "Python yesterday."
+                    "<b> It was wonderful. </b>"
+                    "Perl, <u>I'm leaving you.</u></i>\""
+                    "<br/> The technologies may have changed, but the "
+                    "sentiment remains. We agree Randall;<br /> Edited "
+                    "from <u><a "
+                    "    href='https://xkcd.com/353'>"
+                    "        XKCD/353"
+                    " </a></u> under CC-2.5;"
+                ),
+            )
+        )
+    else:
+        mo.output.append(
+            mo.Html(
+                f"<iframe src='{url}' style='width:100%;height:500px'></iframe>",
+            )
+        )
+    return True
+
+
+def build_browser_fallback() -> "type[webbrowser.BaseBrowser]":
+    """
+    Dynamically create the class since BaseBrowser does not exist in
+    pyodide.
+    """
+
+    # Construct like this to limit stack frames.
+    MarimoBrowser = type(
+        "MarimoBrowser",
+        (webbrowser.BaseBrowser,),
+        {"open": staticmethod(browser_open_fallback)},
+    )
+
+    return MarimoBrowser
diff --git a/marimo/_runtime/patches.py b/marimo/_runtime/patches.py
index e843d1ce707..877dd56d9e1 100644
--- a/marimo/_runtime/patches.py
+++ b/marimo/_runtime/patches.py
@@ -8,7 +8,7 @@
 import types
 from typing import Any, Callable, Iterator
 
-from marimo._runtime import marimo_pdb
+from marimo._runtime import marimo_browser, marimo_pdb
 
 
 def patch_pdb(debugger: marimo_pdb.MarimoPdb) -> None:
@@ -19,6 +19,25 @@ def patch_pdb(debugger: marimo_pdb.MarimoPdb) -> None:
     pdb.set_trace = functools.partial(marimo_pdb.set_trace, debugger=debugger)
 
 
+def patch_webbrowser() -> None:
+    import webbrowser
+
+    try:
+        _ = webbrowser.get()
+    # pyodide doesn't have a webbrowser.get() method
+    # (nor a webbrowser.Error, so careful)
+    except AttributeError:
+        webbrowser.open = marimo_browser.browser_open_fallback
+    except webbrowser.Error:
+        MarimoBrowser = marimo_browser.build_browser_fallback()
+        webbrowser.register(
+            "marimo-output",
+            None,
+            MarimoBrowser(),
+            preferred=True,
+        )
+
+
 def patch_sys_module(module: types.ModuleType) -> None:
     sys.modules[module.__name__] = module
 
diff --git a/marimo/_runtime/runtime.py b/marimo/_runtime/runtime.py
index a741af34b59..0020239ae9b 100644
--- a/marimo/_runtime/runtime.py
+++ b/marimo/_runtime/runtime.py
@@ -537,8 +537,14 @@ def __init__(
         # was invoked. New state updates evict older ones.
         self.state_updates: dict[State[Any], CellId_t] = {}
 
+        # Webbrowser may not be set (e.g. docker container) or stubbed/broken
+        # (e.g. in pyodide). Set default to just inject an iframe of the
+        # expected page to output.
+        patches.patch_webbrowser()
+        # micropip only patched in non-pyodide environments.
         if not is_pyodide():
             patches.patch_micropip(self.globals)
+
         exec("import marimo as __marimo__", self.globals)
 
     def teardown(self) -> None:
diff --git a/tests/_runtime/test_patches.py b/tests/_runtime/test_patches.py
index c2ac7f53848..ca615474d48 100644
--- a/tests/_runtime/test_patches.py
+++ b/tests/_runtime/test_patches.py
@@ -118,3 +118,60 @@ async def test_micropip_set_index_urls(
                     ]
                 )
             TestMicropip._assert_micropip_warning_printed(buf.getvalue())
+
+
+async def test_webbrowser_injection(
+    mocked_kernel: Kernel, exec_req: ExecReqProvider
+):
+    await mocked_kernel.k.run(
+        [
+            exec_req.get("""
+          import webbrowser
+          MarimoBrowser = __marimo__._runtime.marimo_browser.build_browser_fallback()
+          webbrowser.register(
+              "marimo-output", None, MarimoBrowser(), preferred=True
+          )
+          """),
+        ]
+    )
+    await mocked_kernel.k.run(
+        [
+            cell := exec_req.get("webbrowser.open('https://marimo.io');"),
+        ]
+    )
+    assert "webbrowser" in mocked_kernel.k.globals
+    outputs: list[str] = []
+    for msg in mocked_kernel.stream.messages:
+        if msg[0] == "cell-op" and msg[1]["output"] is not None:
+            outputs.append(msg[1]["output"]["data"])
+
+    assert "<iframe" in outputs[-1]
+
+
+async def test_webbrowser_easter_egg(
+    mocked_kernel: Kernel, exec_req: ExecReqProvider
+):
+    await mocked_kernel.k.run(
+        [
+            exec_req.get("""
+          import webbrowser
+          MarimoBrowser = __marimo__._runtime.marimo_browser.build_browser_fallback()
+          webbrowser.register(
+              "marimo-output", None, MarimoBrowser(), preferred=True
+          )
+          """),
+        ]
+    )
+    await mocked_kernel.k.run(
+        [
+            cell := exec_req.get("import antigravity;"),
+        ]
+    )
+    assert "antigravity" in mocked_kernel.k.globals
+    outputs: list[str] = []
+    for msg in mocked_kernel.stream.messages:
+        if msg[0] == "cell-op" and msg[1]["output"] is not None:
+            outputs.append(msg[1]["output"]["data"])
+
+    assert "<iframe" not in outputs[-1]
+    assert "<img" in outputs[-1]