diff --git a/editor.html b/editor.html
index 3cf3ee5..c8ea865 100644
--- a/editor.html
+++ b/editor.html
@@ -1189,14 +1189,13 @@ async function updateFirmware() {   // A/B firmware update over USB-MIDI, with a
   if (!(await _ensureMidi()) || !_midiOutputs().length)
     return alert("Connect the PM_K-1 (Chrome/Edge/Firefox), then try again.");
   const dev = await _queryDeviceVersion();
-  let src;
-  try { src = await (await fetch("/pico-cp-app.py", { cache: "no-store" })).text(); }
-  catch (e) { return alert("Couldn't fetch the latest firmware from the site."); }
+  const src = await _firmwareSource();
+  if (src == null) return;                                   // offline + user cancelled the picker
   const m = src.match(/APP_VERSION\s*=\s*["']([^"']+)["']/); const latest = m && m[1];
-  if (!latest) return alert("Couldn't read the latest firmware version.");
+  if (!latest) return alert("That file isn't PM_K-1 firmware (no APP_VERSION line).");
   const upToDate = dev && dev === latest;
-  if (!confirm("Device firmware: " + (dev || "unknown") + "\nLatest: " + latest +
-      (upToDate ? "\n\nYou're up to date. Re-install anyway?"
+  if (!confirm("Device firmware: " + (dev || "unknown") + "\nNew build: " + latest +
+      (upToDate ? "\n\nSame version. Re-install anyway?"
                 : "\n\nUpdate now? The device reboots, runs the new build, and auto-rolls-back if it fails to start."))) return;
   const bytes = [0xF0, 0x7D, 0x20];
   for (let i = 0; i < src.length; i++) bytes.push(src.charCodeAt(i) & 0x7F);   // app.py is ASCII
@@ -1208,6 +1207,29 @@ async function updateFirmware() {   // A/B firmware update over USB-MIDI, with a
       : ok === false ? "The device is in editor mode (read-only to the updater). Reboot it normally (don't hold A) and try again."
                      : "No acknowledgement from the device. Make sure it's connected and not in editor mode — or drag app.py onto the drive in editor mode.");
 }
+// Where the new app.py comes from: the site when online (the https editor, same-origin), else let the user
+// pick the file — so the OFFLINE editor that ships ON the device can update too (file:// pages can't fetch).
+async function _firmwareSource() {
+  for (const url of ["/pico-cp-app.py", "https://metronome.varasys.io/pico-cp-app.py"]) {
+    try { const r = await fetch(url, { cache: "no-store" }); if (r.ok) return await r.text(); } catch (_) {}
+  }
+  alert("Can't reach the site from this offline copy.\n\nPick the firmware file (app.py) to flash — download it from\n" +
+        "metronome.varasys.io/pico-cp-app.py, or just open the online editor at\nmetronome.varasys.io/editor.html (it updates automatically).");
+  return await _pickFile(".py,text/x-python,text/plain", "PM_K-1 firmware (app.py)", { "text/x-python": [".py"] });
+}
+function _pickFile(accept, desc, fsTypes) {   // resolve to the chosen file's text, or null if cancelled
+  return new Promise(async (res) => {
+    if (window.showOpenFilePicker) {
+      try { const [h] = await showOpenFilePicker({ types: [{ description: desc, accept: fsTypes }] });
+            return res(await (await h.getFile()).text()); }
+      catch (e) { if (e.name === "AbortError") return res(null); }
+    }
+    const inp = document.createElement("input"); inp.type = "file"; inp.accept = accept;
+    inp.onchange = () => { inp.files[0] ? inp.files[0].text().then(res) : res(null); };
+    inp.oncancel = () => res(null);
+    inp.click();
+  });
+}
 
 // Apply a shared link on load. Returns true if it set the metronome state.
 function applyHashShare() {