USB chooser thing aaa

browser/base/content/usbDevicePicker.css

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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#usb-device-picker {
+  min-width: 360px;
+  min-height: 220px;
+}
+
+#picker {
+  padding: 16px;
+}
+
+#message {
+  margin: 0 0 10px;
+}
+
+#devices {
+  min-height: 100px;
+  margin: 0 0 12px;
+}
+
+#buttons {
+  margin-inline-start: 8px;
+}
+
+#buttons > button + button {
+  margin-inline-start: 8px;
+}

browser/base/content/usbDevicePicker.js

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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+var USBDevicePicker = {
+  args: null,
+
+  init() {
+    this.args = window.arguments[0];
+    document.title = this.args.title;
+    document.getElementById("message").value = this.args.message;
+    document.getElementById("select").label = this.args.selectLabel;
+    document.getElementById("cancel").label = this.args.cancelLabel;
+
+    let list = document.getElementById("devices");
+    for (let choice of this.args.choices) {
+      list.appendItem(choice, choice);
+    }
+    list.selectedIndex = 0;
+    list.focus();
+  },
+
+  select() {
+    let list = document.getElementById("devices");
+    this.args.prompt.select(list.selectedIndex);
+  },
+
+  cancel() {
+    this.args.prompt.cancel();
+  },
+
+  destroy() {
+    if (this.args && !this.args.prompt.completed) {
+      // The window manager can close this window directly. Detach it first
+      // so cancel() does not try to close an already-unloading window.
+      this.args.prompt.window = null;
+      this.args.prompt.cancel();
+    }
+    this.args = null;
+  },
+};
+
+window.addEventListener("keydown", event => {
+  if (event.key == "Escape") {
+    USBDevicePicker.cancel();
+  } else if (event.key == "Enter") {
+    USBDevicePicker.select();
+  }
+});

browser/base/content/usbDevicePicker.xul

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+<?xml version="1.0"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
+<?xml-stylesheet href="chrome://browser/content/usbDevicePicker.css" type="text/css"?>
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        id="usb-device-picker" windowtype="Browser:USBDevicePicker"
+        width="420" height="260" onload="USBDevicePicker.init();"
+        onunload="USBDevicePicker.destroy();">
+  <script type="application/javascript" src="chrome://browser/content/usbDevicePicker.js"/>
+  <vbox id="picker" flex="1">
+    <label id="message"/>
+    <listbox id="devices" flex="1" rows="5"
+             ondblclick="USBDevicePicker.select();"/>
+    <hbox id="buttons" pack="end">
+      <button id="cancel" label="Cancel" oncommand="USBDevicePicker.cancel();"/>
+      <button id="select" label="Select" default="true"
+              oncommand="USBDevicePicker.select();"/>
+    </hbox>
+  </vbox>
+</window>