Bug 1654903 - add polyfill for dialog element r?mstriemer draft
authorRobert Helmer <rhelmer@mozilla.com>
Fri, 24 Jul 2020 19:01:34 +0000
changeset 3100967 aa5f04d1bc46f7467a9d998e517fa815cbf235cd
parent 3100966 9fab8ab352bc7f0fb1174dfb06e8c19182645eb1
child 3100968 696df4f81af2c30e749bc009995e69fb627509d7
push id577954
push userbtara@mozilla.com
push dateSun, 02 Aug 2020 09:52:25 +0000
treeherdertry@696df4f81af2 [default view] [failures only]
reviewersmstriemer
bugs1654903
milestone81.0a1
Bug 1654903 - add polyfill for dialog element r?mstriemer Differential Revision: https://phabricator.services.mozilla.com/D84856
browser/components/pioneer/README.md
browser/components/pioneer/content/pioneer.css
browser/components/pioneer/content/pioneer.html
browser/components/pioneer/content/pioneer.js
browser/components/pioneer/content/vendor/dialog-polyfill.css
browser/components/pioneer/content/vendor/dialog-polyfill.js
browser/components/pioneer/jar.mn
tools/rewriting/ThirdPartyPaths.txt
new file mode 100644
--- /dev/null
+++ b/browser/components/pioneer/README.md
@@ -0,0 +1,32 @@
+Pioneer
+=======
+
+This uses revision ee55b3d from https://github.com/GoogleChrome/dialog-polyfill with the following license:
+
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
\ No newline at end of file
--- a/browser/components/pioneer/content/pioneer.css
+++ b/browser/components/pioneer/content/pioneer.css
@@ -102,11 +102,14 @@ details > summary {
 }
 
 .modal > footer {
   display: flex;
   justify-content: flex-end;
   padding-bottom: 16px;
 }
 
-.modal::backdrop {
+.modal::backdrop { /* native */
   background-color: rgba(0,0,0,.5);
 }
+.modal + .backdrop { /* polyfill */
+  background-color: rgba(0,0,0,.5);
+}
--- a/browser/components/pioneer/content/pioneer.html
+++ b/browser/components/pioneer/content/pioneer.html
@@ -9,16 +9,18 @@
     <meta http-equiv="Content-Security-Policy" content="default-src chrome: blob:; img-src https:; object-src 'none'">
     <link rel="localization" href="browser/branding/brandings.ftl">
     <link rel="localization" href="branding/brand.ftl">
     <!-- Temporary "en-US"-only l10n strings -->
     <link rel="localization" href="preview/pioneer.ftl">
     <link rel="stylesheet" href="chrome://global/skin/in-content/common.css">
     <link rel="stylesheet" href="chrome://global/skin/in-content/toggle-button.css">
     <link rel="stylesheet" href="chrome://browser/content/pioneer.css">
+    <link rel="stylesheet" href="chrome://browser/content/vendor/dialog-polyfill.css">
+    <script src="chrome://browser/content/vendor/dialog-polyfill.js"></script>
     <script src="chrome://browser/content/pioneer.js"></script>
     <link rel="icon" href="chrome://browser/skin/pioneer.svg">
     <title data-l10n-id="pioneer"></title>
   </head>
 
   <body>
     <div id="report-content">
       <button id="enrollment-button" class="primary"></button>
--- a/browser/components/pioneer/content/pioneer.js
+++ b/browser/components/pioneer/content/pioneer.js
@@ -227,16 +227,18 @@ async function setup(cachedAddons) {
           const study = document.getElementById(cachedAddon.addon_id);
           if (study) {
             await updateStudy(cachedAddon.addon_id);
           }
         }
         showEnrollmentStatus();
       } else {
         let dialog = document.querySelector("dialog");
+        // eslint-disable-next-line no-undef
+        dialogPolyfill.registerDialog(dialog);
         dialog.showModal();
         dialog.scrollTop = 0;
       }
     });
 
   document
     .getElementById("cancel-dialog-button")
     .addEventListener("click", () => document.querySelector("dialog").close());
new file mode 100644
--- /dev/null
+++ b/browser/components/pioneer/content/vendor/dialog-polyfill.css
@@ -0,0 +1,37 @@
+dialog {
+  position: absolute;
+  left: 0; right: 0;
+  width: -moz-fit-content;
+  width: -webkit-fit-content;
+  width: fit-content;
+  height: -moz-fit-content;
+  height: -webkit-fit-content;
+  height: fit-content;
+  margin: auto;
+  border: solid;
+  padding: 1em;
+  background: white;
+  color: black;
+  display: block;
+}
+
+dialog:not([open]) {
+  display: none;
+}
+
+dialog + .backdrop {
+  position: fixed;
+  top: 0; right: 0; bottom: 0; left: 0;
+  background: rgba(0,0,0,0.1);
+}
+
+._dialog_overlay {
+  position: fixed;
+  top: 0; right: 0; bottom: 0; left: 0;
+}
+
+dialog.fixed {
+  position: fixed;
+  top: 50%;
+  transform: translate(0, -50%);
+}
\ No newline at end of file
new file mode 100644
--- /dev/null
+++ b/browser/components/pioneer/content/vendor/dialog-polyfill.js
@@ -0,0 +1,870 @@
+(function(global, factory) {
+  typeof exports === "object" && typeof module !== "undefined"
+    ? (module.exports = factory())
+    : typeof define === "function" && define.amd
+    ? define(factory)
+    : ((global = global || self), (global.dialogPolyfill = factory()));
+})(this, function() {
+  "use strict";
+
+  // nb. This is for IE10 and lower _only_.
+  var supportCustomEvent = window.CustomEvent;
+  if (!supportCustomEvent || typeof supportCustomEvent === "object") {
+    supportCustomEvent = function CustomEvent(event, x) {
+      x = x || {};
+      var ev = document.createEvent("CustomEvent");
+      ev.initCustomEvent(event, !!x.bubbles, !!x.cancelable, x.detail || null);
+      return ev;
+    };
+    supportCustomEvent.prototype = window.Event.prototype;
+  }
+
+  /**
+   * @param {Element} el to check for stacking context
+   * @return {boolean} whether this el or its parents creates a stacking context
+   */
+  function createsStackingContext(el) {
+    while (el && el !== document.body) {
+      var s = window.getComputedStyle(el);
+      var invalid = function(k, ok) {
+        return !(s[k] === undefined || s[k] === ok);
+      };
+
+      if (
+        s.opacity < 1 ||
+        invalid("zIndex", "auto") ||
+        invalid("transform", "none") ||
+        invalid("mixBlendMode", "normal") ||
+        invalid("filter", "none") ||
+        invalid("perspective", "none") ||
+        s.isolation === "isolate" ||
+        s.position === "fixed" ||
+        s.webkitOverflowScrolling === "touch"
+      ) {
+        return true;
+      }
+      el = el.parentElement;
+    }
+    return false;
+  }
+
+  /**
+   * Finds the nearest <dialog> from the passed element.
+   *
+   * @param {Element} el to search from
+   * @return {HTMLDialogElement} dialog found
+   */
+  function findNearestDialog(el) {
+    while (el) {
+      if (el.localName === "dialog") {
+        return /** @type {HTMLDialogElement} */ (el);
+      }
+      el = el.parentElement;
+    }
+    return null;
+  }
+
+  /**
+   * Blur the specified element, as long as it's not the HTML body element.
+   * This works around an IE9/10 bug - blurring the body causes Windows to
+   * blur the whole application.
+   *
+   * @param {Element} el to blur
+   */
+  function safeBlur(el) {
+    // Find the actual focused element when the active element is inside a shadow root
+    while (el && el.shadowRoot && el.shadowRoot.activeElement) {
+      el = el.shadowRoot.activeElement;
+    }
+
+    if (el && el.blur && el !== document.body) {
+      el.blur();
+    }
+  }
+
+  /**
+   * @param {!NodeList} nodeList to search
+   * @param {Node} node to find
+   * @return {boolean} whether node is inside nodeList
+   */
+  function inNodeList(nodeList, node) {
+    for (var i = 0; i < nodeList.length; ++i) {
+      if (nodeList[i] === node) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * @param {HTMLFormElement} el to check
+   * @return {boolean} whether this form has method="dialog"
+   */
+  function isFormMethodDialog(el) {
+    if (!el || !el.hasAttribute("method")) {
+      return false;
+    }
+    return el.getAttribute("method").toLowerCase() === "dialog";
+  }
+
+  /**
+   * @param {!DocumentFragment|!Element} hostElement
+   * @return {?Element}
+   */
+  function findFocusableElementWithin(hostElement) {
+    // Note that this is 'any focusable area'. This list is probably not exhaustive, but the
+    // alternative involves stepping through and trying to focus everything.
+    var opts = ["button", "input", "keygen", "select", "textarea"];
+    var query = opts.map(function(el) {
+      return el + ":not([disabled])";
+    });
+    // TODO(samthor): tabindex values that are not numeric are not focusable.
+    query.push('[tabindex]:not([disabled]):not([tabindex=""])'); // tabindex != "", not disabled
+    var target = hostElement.querySelector(query.join(", "));
+
+    if (!target && "attachShadow" in Element.prototype) {
+      // If we haven't found a focusable target, see if the host element contains an element
+      // which has a shadowRoot.
+      // Recursively search for the first focusable item in shadow roots.
+      var elems = hostElement.querySelectorAll("*");
+      for (var i = 0; i < elems.length; i++) {
+        if (elems[i].tagName && elems[i].shadowRoot) {
+          target = findFocusableElementWithin(elems[i].shadowRoot);
+          if (target) {
+            break;
+          }
+        }
+      }
+    }
+    return target;
+  }
+
+  /**
+   * Determines if an element is attached to the DOM.
+   * @param {Element} element to check
+   * @return {Boolean} whether the element is in DOM
+   */
+  function isConnected(element) {
+    return element.isConnected || document.body.contains(element);
+  }
+
+  /**
+   * @param {!HTMLDialogElement} dialog to upgrade
+   * @constructor
+   */
+  function dialogPolyfillInfo(dialog) {
+    this.dialog_ = dialog;
+    this.replacedStyleTop_ = false;
+    this.openAsModal_ = false;
+
+    // Set a11y role. Browsers that support dialog implicitly know this already.
+    if (!dialog.hasAttribute("role")) {
+      dialog.setAttribute("role", "dialog");
+    }
+
+    dialog.show = this.show.bind(this);
+    dialog.showModal = this.showModal.bind(this);
+    dialog.close = this.close.bind(this);
+
+    if (!("returnValue" in dialog)) {
+      dialog.returnValue = "";
+    }
+
+    if ("MutationObserver" in window) {
+      var mo = new MutationObserver(this.maybeHideModal.bind(this));
+      mo.observe(dialog, { attributes: true, attributeFilter: ["open"] });
+    } else {
+      // IE10 and below support. Note that DOMNodeRemoved etc fire _before_ removal. They also
+      // seem to fire even if the element was removed as part of a parent removal. Use the removed
+      // events to force downgrade (useful if removed/immediately added).
+      var removed = false;
+      var cb = function() {
+        removed ? this.downgradeModal() : this.maybeHideModal();
+        removed = false;
+      }.bind(this);
+      var timeout;
+      var delayModel = function(ev) {
+        if (ev.target !== dialog) {
+          return;
+        } // not for a child element
+        var cand = "DOMNodeRemoved";
+        removed |= ev.type.substr(0, cand.length) === cand;
+        window.clearTimeout(timeout);
+        timeout = window.setTimeout(cb, 0);
+      };
+      [
+        "DOMAttrModified",
+        "DOMNodeRemoved",
+        "DOMNodeRemovedFromDocument",
+      ].forEach(function(name) {
+        dialog.addEventListener(name, delayModel);
+      });
+    }
+    // Note that the DOM is observed inside DialogManager while any dialog
+    // is being displayed as a modal, to catch modal removal from the DOM.
+
+    Object.defineProperty(dialog, "open", {
+      set: this.setOpen.bind(this),
+      get: dialog.hasAttribute.bind(dialog, "open"),
+    });
+
+    this.backdrop_ = document.createElement("div");
+    this.backdrop_.className = "backdrop";
+    this.backdrop_.addEventListener("click", this.backdropClick_.bind(this));
+  }
+
+  dialogPolyfillInfo.prototype = /** @type {HTMLDialogElement.prototype} */ ({
+    get dialog() {
+      return this.dialog_;
+    },
+
+    /**
+     * Maybe remove this dialog from the modal top layer. This is called when
+     * a modal dialog may no longer be tenable, e.g., when the dialog is no
+     * longer open or is no longer part of the DOM.
+     */
+    maybeHideModal() {
+      if (this.dialog_.hasAttribute("open") && isConnected(this.dialog_)) {
+        return;
+      }
+      this.downgradeModal();
+    },
+
+    /**
+     * Remove this dialog from the modal top layer, leaving it as a non-modal.
+     */
+    downgradeModal() {
+      if (!this.openAsModal_) {
+        return;
+      }
+      this.openAsModal_ = false;
+      this.dialog_.style.zIndex = "";
+
+      // This won't match the native <dialog> exactly because if the user set top on a centered
+      // polyfill dialog, that top gets thrown away when the dialog is closed. Not sure it's
+      // possible to polyfill this perfectly.
+      if (this.replacedStyleTop_) {
+        this.dialog_.style.top = "";
+        this.replacedStyleTop_ = false;
+      }
+
+      // Clear the backdrop and remove from the manager.
+      this.backdrop_.parentNode &&
+        this.backdrop_.parentNode.removeChild(this.backdrop_);
+      dialogPolyfill.dm.removeDialog(this);
+    },
+
+    /**
+     * @param {boolean} value whether to open or close this dialog
+     */
+    setOpen(value) {
+      if (value) {
+        this.dialog_.hasAttribute("open") ||
+          this.dialog_.setAttribute("open", "");
+      } else {
+        this.dialog_.removeAttribute("open");
+        this.maybeHideModal(); // nb. redundant with MutationObserver
+      }
+    },
+
+    /**
+     * Handles clicks on the fake .backdrop element, redirecting them as if
+     * they were on the dialog itself.
+     *
+     * @param {!Event} e to redirect
+     */
+    backdropClick_(e) {
+      if (!this.dialog_.hasAttribute("tabindex")) {
+        // Clicking on the backdrop should move the implicit cursor, even if dialog cannot be
+        // focused. Create a fake thing to focus on. If the backdrop was _before_ the dialog, this
+        // would not be needed - clicks would move the implicit cursor there.
+        var fake = document.createElement("div");
+        this.dialog_.insertBefore(fake, this.dialog_.firstChild);
+        fake.tabIndex = -1;
+        fake.focus();
+        this.dialog_.removeChild(fake);
+      } else {
+        this.dialog_.focus();
+      }
+
+      var redirectedEvent = document.createEvent("MouseEvents");
+      redirectedEvent.initMouseEvent(
+        e.type,
+        e.bubbles,
+        e.cancelable,
+        window,
+        e.detail,
+        e.screenX,
+        e.screenY,
+        e.clientX,
+        e.clientY,
+        e.ctrlKey,
+        e.altKey,
+        e.shiftKey,
+        e.metaKey,
+        e.button,
+        e.relatedTarget
+      );
+      this.dialog_.dispatchEvent(redirectedEvent);
+      e.stopPropagation();
+    },
+
+    /**
+     * Focuses on the first focusable element within the dialog. This will always blur the current
+     * focus, even if nothing within the dialog is found.
+     */
+    focus_() {
+      // Find element with `autofocus` attribute, or fall back to the first form/tabindex control.
+      var target = this.dialog_.querySelector("[autofocus]:not([disabled])");
+      if (!target && this.dialog_.tabIndex >= 0) {
+        target = this.dialog_;
+      }
+      if (!target) {
+        target = findFocusableElementWithin(this.dialog_);
+      }
+      safeBlur(document.activeElement);
+      target && target.focus();
+    },
+
+    /**
+     * Sets the zIndex for the backdrop and dialog.
+     *
+     * @param {number} dialogZ
+     * @param {number} backdropZ
+     */
+    updateZIndex(dialogZ, backdropZ) {
+      if (dialogZ < backdropZ) {
+        throw new Error("dialogZ should never be < backdropZ");
+      }
+      this.dialog_.style.zIndex = dialogZ;
+      this.backdrop_.style.zIndex = backdropZ;
+    },
+
+    /**
+     * Shows the dialog. If the dialog is already open, this does nothing.
+     */
+    show() {
+      if (!this.dialog_.open) {
+        this.setOpen(true);
+        this.focus_();
+      }
+    },
+
+    /**
+     * Show this dialog modally.
+     */
+    showModal() {
+      if (this.dialog_.hasAttribute("open")) {
+        throw new Error(
+          "Failed to execute 'showModal' on dialog: The element is already open, and therefore cannot be opened modally."
+        );
+      }
+      if (!isConnected(this.dialog_)) {
+        throw new Error(
+          "Failed to execute 'showModal' on dialog: The element is not in a Document."
+        );
+      }
+      if (!dialogPolyfill.dm.pushDialog(this)) {
+        throw new Error(
+          "Failed to execute 'showModal' on dialog: There are too many open modal dialogs."
+        );
+      }
+
+      if (createsStackingContext(this.dialog_.parentElement)) {
+        console.warn(
+          "A dialog is being shown inside a stacking context. " +
+            "This may cause it to be unusable. For more information, see this link: " +
+            "https://github.com/GoogleChrome/dialog-polyfill/#stacking-context"
+        );
+      }
+
+      this.setOpen(true);
+      this.openAsModal_ = true;
+
+      // Optionally center vertically, relative to the current viewport.
+      if (dialogPolyfill.needsCentering(this.dialog_)) {
+        dialogPolyfill.reposition(this.dialog_);
+        this.replacedStyleTop_ = true;
+      } else {
+        this.replacedStyleTop_ = false;
+      }
+
+      // Insert backdrop.
+      this.dialog_.parentNode.insertBefore(
+        this.backdrop_,
+        this.dialog_.nextSibling
+      );
+
+      // Focus on whatever inside the dialog.
+      this.focus_();
+    },
+
+    /**
+     * Closes this HTMLDialogElement. This is optional vs clearing the open
+     * attribute, however this fires a 'close' event.
+     *
+     * @param {string=} opt_returnValue to use as the returnValue
+     */
+    close(opt_returnValue) {
+      if (!this.dialog_.hasAttribute("open")) {
+        throw new Error(
+          "Failed to execute 'close' on dialog: The element does not have an 'open' attribute, and therefore cannot be closed."
+        );
+      }
+      this.setOpen(false);
+
+      // Leave returnValue untouched in case it was set directly on the element
+      if (opt_returnValue !== undefined) {
+        this.dialog_.returnValue = opt_returnValue;
+      }
+
+      // Triggering "close" event for any attached listeners on the <dialog>.
+      var closeEvent = new supportCustomEvent("close", {
+        bubbles: false,
+        cancelable: false,
+      });
+      this.dialog_.dispatchEvent(closeEvent);
+    },
+  });
+
+  var dialogPolyfill = {};
+
+  dialogPolyfill.reposition = function(element) {
+    var scrollTop =
+      document.body.scrollTop || document.documentElement.scrollTop;
+    var topValue = scrollTop + (window.innerHeight - element.offsetHeight) / 2;
+    element.style.top = Math.max(scrollTop, topValue) + "px";
+  };
+
+  dialogPolyfill.isInlinePositionSetByStylesheet = function(element) {
+    for (var i = 0; i < document.styleSheets.length; ++i) {
+      var styleSheet = document.styleSheets[i];
+      var cssRules = null;
+      // Some browsers throw on cssRules.
+      try {
+        cssRules = styleSheet.cssRules;
+      } catch (e) {}
+      if (!cssRules) {
+        continue;
+      }
+      for (var j = 0; j < cssRules.length; ++j) {
+        var rule = cssRules[j];
+        var selectedNodes = null;
+        // Ignore errors on invalid selector texts.
+        try {
+          selectedNodes = document.querySelectorAll(rule.selectorText);
+        } catch (e) {}
+        if (!selectedNodes || !inNodeList(selectedNodes, element)) {
+          continue;
+        }
+        var cssTop = rule.style.getPropertyValue("top");
+        var cssBottom = rule.style.getPropertyValue("bottom");
+        if (
+          (cssTop && cssTop !== "auto") ||
+          (cssBottom && cssBottom !== "auto")
+        ) {
+          return true;
+        }
+      }
+    }
+    return false;
+  };
+
+  dialogPolyfill.needsCentering = function(dialog) {
+    var computedStyle = window.getComputedStyle(dialog);
+    if (computedStyle.position !== "absolute") {
+      return false;
+    }
+
+    // We must determine whether the top/bottom specified value is non-auto.  In
+    // WebKit/Blink, checking computedStyle.top == 'auto' is sufficient, but
+    // Firefox returns the used value. So we do this crazy thing instead: check
+    // the inline style and then go through CSS rules.
+    if (
+      (dialog.style.top !== "auto" && dialog.style.top !== "") ||
+      (dialog.style.bottom !== "auto" && dialog.style.bottom !== "")
+    ) {
+      return false;
+    }
+    return !dialogPolyfill.isInlinePositionSetByStylesheet(dialog);
+  };
+
+  /**
+   * @param {!Element} element to force upgrade
+   */
+  dialogPolyfill.forceRegisterDialog = function(element) {
+    if (window.HTMLDialogElement || element.showModal) {
+      console.warn(
+        "This browser already supports <dialog>, the polyfill " +
+          "may not work correctly",
+        element
+      );
+    }
+    if (element.localName !== "dialog") {
+      throw new Error(
+        "Failed to register dialog: The element is not a dialog."
+      );
+    }
+    new dialogPolyfillInfo(/** @type {!HTMLDialogElement} */ (element));
+  };
+
+  /**
+   * @param {!Element} element to upgrade, if necessary
+   */
+  dialogPolyfill.registerDialog = function(element) {
+    if (!element.showModal) {
+      dialogPolyfill.forceRegisterDialog(element);
+    }
+  };
+
+  /**
+   * @constructor
+   */
+  dialogPolyfill.DialogManager = function() {
+    /** @type {!Array<!dialogPolyfillInfo>} */
+    this.pendingDialogStack = [];
+
+    var checkDOM = this.checkDOM_.bind(this);
+
+    // The overlay is used to simulate how a modal dialog blocks the document.
+    // The blocking dialog is positioned on top of the overlay, and the rest of
+    // the dialogs on the pending dialog stack are positioned below it. In the
+    // actual implementation, the modal dialog stacking is controlled by the
+    // top layer, where z-index has no effect.
+    this.overlay = document.createElement("div");
+    this.overlay.className = "_dialog_overlay";
+    this.overlay.addEventListener(
+      "click",
+      function(e) {
+        this.forwardTab_ = undefined;
+        e.stopPropagation();
+        checkDOM([]); // sanity-check DOM
+      }.bind(this)
+    );
+
+    this.handleKey_ = this.handleKey_.bind(this);
+    this.handleFocus_ = this.handleFocus_.bind(this);
+
+    this.zIndexLow_ = 100000;
+    this.zIndexHigh_ = 100000 + 150;
+
+    this.forwardTab_ = undefined;
+
+    if ("MutationObserver" in window) {
+      this.mo_ = new MutationObserver(function(records) {
+        var removed = [];
+        records.forEach(function(rec) {
+          for (var i = 0, c; (c = rec.removedNodes[i]); ++i) {
+            if (!(c instanceof Element)) {
+              continue;
+            } else if (c.localName === "dialog") {
+              removed.push(c);
+            }
+            removed = removed.concat(c.querySelectorAll("dialog"));
+          }
+        });
+        removed.length && checkDOM(removed);
+      });
+    }
+  };
+
+  /**
+   * Called on the first modal dialog being shown. Adds the overlay and related
+   * handlers.
+   */
+  dialogPolyfill.DialogManager.prototype.blockDocument = function() {
+    document.documentElement.addEventListener("focus", this.handleFocus_, true);
+    document.addEventListener("keydown", this.handleKey_);
+    this.mo_ && this.mo_.observe(document, { childList: true, subtree: true });
+  };
+
+  /**
+   * Called on the first modal dialog being removed, i.e., when no more modal
+   * dialogs are visible.
+   */
+  dialogPolyfill.DialogManager.prototype.unblockDocument = function() {
+    document.documentElement.removeEventListener(
+      "focus",
+      this.handleFocus_,
+      true
+    );
+    document.removeEventListener("keydown", this.handleKey_);
+    this.mo_ && this.mo_.disconnect();
+  };
+
+  /**
+   * Updates the stacking of all known dialogs.
+   */
+  dialogPolyfill.DialogManager.prototype.updateStacking = function() {
+    var zIndex = this.zIndexHigh_;
+
+    for (var i = 0, dpi; (dpi = this.pendingDialogStack[i]); ++i) {
+      dpi.updateZIndex(--zIndex, --zIndex);
+      if (i === 0) {
+        this.overlay.style.zIndex = --zIndex;
+      }
+    }
+
+    // Make the overlay a sibling of the dialog itself.
+    var last = this.pendingDialogStack[0];
+    if (last) {
+      var p = last.dialog.parentNode || document.body;
+      p.appendChild(this.overlay);
+    } else if (this.overlay.parentNode) {
+      this.overlay.parentNode.removeChild(this.overlay);
+    }
+  };
+
+  /**
+   * @param {Element} candidate to check if contained or is the top-most modal dialog
+   * @return {boolean} whether candidate is contained in top dialog
+   */
+  dialogPolyfill.DialogManager.prototype.containedByTopDialog_ = function(
+    candidate
+  ) {
+    while ((candidate = findNearestDialog(candidate))) {
+      for (var i = 0, dpi; (dpi = this.pendingDialogStack[i]); ++i) {
+        if (dpi.dialog === candidate) {
+          return i === 0; // only valid if top-most
+        }
+      }
+      candidate = candidate.parentElement;
+    }
+    return false;
+  };
+
+  dialogPolyfill.DialogManager.prototype.handleFocus_ = function(event) {
+    var target = event.composedPath ? event.composedPath()[0] : event.target;
+
+    if (this.containedByTopDialog_(target)) {
+      return;
+    }
+
+    if (document.activeElement === document.documentElement) {
+      return;
+    }
+
+    event.preventDefault();
+    event.stopPropagation();
+    safeBlur(/** @type {Element} */ (target));
+
+    if (this.forwardTab_ === undefined) {
+      return;
+    } // move focus only from a tab key
+
+    var dpi = this.pendingDialogStack[0];
+    var dialog = dpi.dialog;
+    var position = dialog.compareDocumentPosition(target);
+    if (position & Node.DOCUMENT_POSITION_PRECEDING) {
+      if (this.forwardTab_) {
+        // forward
+        dpi.focus_();
+      } else if (target !== document.documentElement) {
+        // backwards if we're not already focused on <html>
+        document.documentElement.focus();
+      }
+    }
+
+    return false;
+  };
+
+  dialogPolyfill.DialogManager.prototype.handleKey_ = function(event) {
+    this.forwardTab_ = undefined;
+    if (event.keyCode === 27) {
+      event.preventDefault();
+      event.stopPropagation();
+      var cancelEvent = new supportCustomEvent("cancel", {
+        bubbles: false,
+        cancelable: true,
+      });
+      var dpi = this.pendingDialogStack[0];
+      if (dpi && dpi.dialog.dispatchEvent(cancelEvent)) {
+        dpi.dialog.close();
+      }
+    } else if (event.keyCode === 9) {
+      this.forwardTab_ = !event.shiftKey;
+    }
+  };
+
+  /**
+   * Finds and downgrades any known modal dialogs that are no longer displayed. Dialogs that are
+   * removed and immediately readded don't stay modal, they become normal.
+   *
+   * @param {!Array<!HTMLDialogElement>} removed that have definitely been removed
+   */
+  dialogPolyfill.DialogManager.prototype.checkDOM_ = function(removed) {
+    // This operates on a clone because it may cause it to change. Each change also calls
+    // updateStacking, which only actually needs to happen once. But who removes many modal dialogs
+    // at a time?!
+    var clone = this.pendingDialogStack.slice();
+    clone.forEach(function(dpi) {
+      if (removed.indexOf(dpi.dialog) !== -1) {
+        dpi.downgradeModal();
+      } else {
+        dpi.maybeHideModal();
+      }
+    });
+  };
+
+  /**
+   * @param {!dialogPolyfillInfo} dpi
+   * @return {boolean} whether the dialog was allowed
+   */
+  dialogPolyfill.DialogManager.prototype.pushDialog = function(dpi) {
+    var allowed = (this.zIndexHigh_ - this.zIndexLow_) / 2 - 1;
+    if (this.pendingDialogStack.length >= allowed) {
+      return false;
+    }
+    if (this.pendingDialogStack.unshift(dpi) === 1) {
+      this.blockDocument();
+    }
+    this.updateStacking();
+    return true;
+  };
+
+  /**
+   * @param {!dialogPolyfillInfo} dpi
+   */
+  dialogPolyfill.DialogManager.prototype.removeDialog = function(dpi) {
+    var index = this.pendingDialogStack.indexOf(dpi);
+    if (index === -1) {
+      return;
+    }
+
+    this.pendingDialogStack.splice(index, 1);
+    if (this.pendingDialogStack.length === 0) {
+      this.unblockDocument();
+    }
+    this.updateStacking();
+  };
+
+  dialogPolyfill.dm = new dialogPolyfill.DialogManager();
+  dialogPolyfill.formSubmitter = null;
+  dialogPolyfill.useValue = null;
+
+  /**
+   * Installs global handlers, such as click listers and native method overrides. These are needed
+   * even if a no dialog is registered, as they deal with <form method="dialog">.
+   */
+  if (window.HTMLDialogElement === undefined) {
+    /**
+     * If HTMLFormElement translates method="DIALOG" into 'get', then replace the descriptor with
+     * one that returns the correct value.
+     */
+    var testForm = document.createElement("form");
+    testForm.setAttribute("method", "dialog");
+    if (testForm.method !== "dialog") {
+      var methodDescriptor = Object.getOwnPropertyDescriptor(
+        HTMLFormElement.prototype,
+        "method"
+      );
+      if (methodDescriptor) {
+        // nb. Some older iOS and older PhantomJS fail to return the descriptor. Don't do anything
+        // and don't bother to update the element.
+        var realGet = methodDescriptor.get;
+        methodDescriptor.get = function() {
+          if (isFormMethodDialog(this)) {
+            return "dialog";
+          }
+          return realGet.call(this);
+        };
+        var realSet = methodDescriptor.set;
+        /** @this {HTMLElement} */
+        methodDescriptor.set = function(v) {
+          if (typeof v === "string" && v.toLowerCase() === "dialog") {
+            return this.setAttribute("method", v);
+          }
+          return realSet.call(this, v);
+        };
+        Object.defineProperty(
+          HTMLFormElement.prototype,
+          "method",
+          methodDescriptor
+        );
+      }
+    }
+
+    /**
+     * Global 'click' handler, to capture the <input type="submit"> or <button> element which has
+     * submitted a <form method="dialog">. Needed as Safari and others don't report this inside
+     * document.activeElement.
+     */
+    document.addEventListener("click", function(ev) {
+      dialogPolyfill.formSubmitter = null;
+      dialogPolyfill.useValue = null;
+      if (ev.defaultPrevented) {
+        return;
+      } // e.g. a submit which prevents default submission
+
+      var target = /** @type {Element} */ (ev.target);
+      if (!target || !isFormMethodDialog(target.form)) {
+        return;
+      }
+
+      var valid =
+        target.type === "submit" &&
+        ["button", "input"].indexOf(target.localName) > -1;
+      if (!valid) {
+        if (!(target.localName === "input" && target.type === "image")) {
+          return;
+        }
+        // this is a <input type="image">, which can submit forms
+        dialogPolyfill.useValue = ev.offsetX + "," + ev.offsetY;
+      }
+
+      var dialog = findNearestDialog(target);
+      if (!dialog) {
+        return;
+      }
+
+      dialogPolyfill.formSubmitter = target;
+    });
+
+    /**
+     * Replace the native HTMLFormElement.submit() method, as it won't fire the
+     * submit event and give us a chance to respond.
+     */
+    var nativeFormSubmit = HTMLFormElement.prototype.submit;
+    var replacementFormSubmit = function() {
+      if (!isFormMethodDialog(this)) {
+        return nativeFormSubmit.call(this);
+      }
+      var dialog = findNearestDialog(this);
+      dialog && dialog.close();
+    };
+    HTMLFormElement.prototype.submit = replacementFormSubmit;
+
+    /**
+     * Global form 'dialog' method handler. Closes a dialog correctly on submit
+     * and possibly sets its return value.
+     */
+    document.addEventListener("submit", function(ev) {
+      if (ev.defaultPrevented) {
+        return;
+      } // e.g. a submit which prevents default submission
+
+      var form = /** @type {HTMLFormElement} */ (ev.target);
+      if (!isFormMethodDialog(form)) {
+        return;
+      }
+      ev.preventDefault();
+
+      var dialog = findNearestDialog(form);
+      if (!dialog) {
+        return;
+      }
+
+      // Forms can only be submitted via .submit() or a click (?), but anyway: sanity-check that
+      // the submitter is correct before using its value as .returnValue.
+      var s = dialogPolyfill.formSubmitter;
+      if (s && s.form === form) {
+        dialog.close(dialogPolyfill.useValue || s.value);
+      } else {
+        dialog.close();
+      }
+      dialogPolyfill.formSubmitter = null;
+    });
+  }
+
+  return dialogPolyfill;
+});
--- a/browser/components/pioneer/jar.mn
+++ b/browser/components/pioneer/jar.mn
@@ -1,8 +1,10 @@
 # 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/.
 
 browser.jar:
     content/browser/pioneer.html                      (content/pioneer.html)
     content/browser/pioneer.css                       (content/pioneer.css)
     content/browser/pioneer.js                        (content/pioneer.js)
+    content/browser/vendor/dialog-polyfill.css        (content/vendor/dialog-polyfill.css)
+    content/browser/vendor/dialog-polyfill.js         (content/vendor/dialog-polyfill.js)
--- a/tools/rewriting/ThirdPartyPaths.txt
+++ b/tools/rewriting/ThirdPartyPaths.txt
@@ -1,9 +1,10 @@
 browser/components/newtab/vendor/
+browser/components/pioneer/content/vendor/
 browser/components/pocket/content/panels/js/vendor/
 browser/components/translation/cld2/
 browser/extensions/formautofill/content/third-party/
 browser/extensions/screenshots/build/raven.js
 devtools/client/debugger/flow-typed/npm/
 devtools/client/inspector/markup/test/lib_*
 devtools/client/jsonview/lib/require.js
 devtools/client/shared/demangle.js