Firefox源码试读之一： 何处决定新链接或书签是新标签页还是新窗口，当前窗口打开

    以前的版本，点击书签，可以新标签页打开，新的42.0没有配置选项，又不想安装扩展组件，很是困惑Firefox为什么不做配置项。于是下载了42.0的源代码，自己找找。

    初看源代码，不知道从何处下手，经过一番摸索，觉得书签点击类操作应该在browser目录下，果然找到了。

(1) browser\base\content\browser.js(998)

  var gBrowserInit = {
  delayedStartupFinished: false,

  onLoad: function() {
    gBrowser.addEventListener("DOMUpdatePageReport", gPopupBlockerObserver, false);

    Services.obs.addObserver(gPluginHandler.NPAPIPluginCrashed, "plugin-crashed", false);

    window.addEventListener("AppCommand", HandleAppCommandEvent, true);

    // These routines add message listeners. They must run before
    // loading the frame script to ensure that we don't miss any
    // message sent between when the frame script is loaded and when
    // the listener is registered.
    DOMLinkHandler.init();
    gPageStyleMenu.init();
    LanguageDetectionListener.init();
    BrowserOnClick.init();
    DevEdition.init();
    AboutPrivateBrowsingListener.init();
    TrackingProtection.init();

    let mm = window.getGroupMessageManager("browsers");
    mm.loadFrameScript("chrome://browser/content/tab-content.js", true);
    mm.loadFrameScript("chrome://browser/content/content.js", true);
    mm.loadFrameScript("chrome://browser/content/content-UITour.js", true);
    mm.loadFrameScript("chrome://global/content/manifestMessages.js", true);

    window.messageManager.addMessageListener("Browser:LoadURI", RedirectLoad);

    // initialize observers and listeners
    // and give C++ access to gBrowser
    XULBrowserWindow.init();
    window.QueryInterface(Ci.nsIInterfaceRequestor)
          .getInterface(nsIWebNavigation)
          .QueryInterface(Ci.nsIDocShellTreeItem).treeOwner
          .QueryInterface(Ci.nsIInterfaceRequestor)
          .getInterface(Ci.nsIXULWindow)
          .XULBrowserWindow = window.XULBrowserWindow;
    window.QueryInterface(Ci.nsIDOMChromeWindow).browserDOMWindow =
      new nsBrowserAccess();

    if (!gMultiProcessBrowser) {
      // There is a Content:Click message manually sent from content.
      Cc["@mozilla.org/eventlistenerservice;1"]
        .getService(Ci.nsIEventListenerService)
        .addSystemEventListener(gBrowser, "click", contentAreaClick, true);
    }

    ...

/**
 * Called whenever the user clicks in the content area.
 *
 * @param event
 *        The click event.
 * @param isPanelClick
 *        Whether the event comes from a web panel.
 * @note default event is prevented if the click is handled.
 */
function contentAreaClick(event, isPanelClick)
{
  if (!event.isTrusted || event.defaultPrevented || event.button == 2)
    return;

  let [href, linkNode] = hrefAndLinkNodeForClickEvent(event);
  if (!href) {
    // Not a link, handle middle mouse navigation.
    if (event.button == 1 &&
        gPrefService.getBoolPref("middlemouse.contentLoadURL") &&
        !gPrefService.getBoolPref("general.autoScroll")) {
      middleMousePaste(event);
      event.preventDefault();
    }
    return;
  }

  // This code only applies if we have a linkNode (i.e. clicks on real anchor
  // elements, as opposed to XLink).
  if (linkNode && event.button == 0 &&
      !event.ctrlKey && !event.shiftKey && !event.altKey && !event.metaKey) {
    // A Web panel's links should target the main content area.  Do this
    // if no modifier keys are down and if there's no target or the target
    // equals _main (the IE convention) or _content (the Mozilla convention).
    let target = linkNode.target;
    let mainTarget = !target || target == "_content" || target  == "_main";
    if (isPanelClick && mainTarget) {
      // javascript and data links should be executed in the current browser.
      if (linkNode.getAttribute("onclick") ||
          href.startsWith("javascript:") ||
          href.startsWith("data:"))
        return;

      try {
        urlSecurityCheck(href, linkNode.ownerDocument.nodePrincipal);
      }
      catch(ex) {
        // Prevent loading unsecure destinations.
        event.preventDefault();
        return;
      }

      loadURI(href, null, null, false);
      event.preventDefault();
      return;
    }

    if (linkNode.getAttribute("rel") == "sidebar") {
      // This is the Opera convention for a special link that, when clicked,
      // allows to add a sidebar panel.  The link's title attribute contains
      // the title that should be used for the sidebar panel.
      PlacesUIUtils.showBookmarkDialog({ action: "add"
                                       , type: "bookmark"
                                       , uri: makeURI(href)
                                       , title: linkNode.getAttribute("title")
                                       , loadBookmarkInSidebar: true
                                       , hiddenRows: [ "description", "location", "keyword" ]
                                       }, window);
      event.preventDefault();
      return;
    }
  }

  handleLinkClick(event, href, linkNode);

  // Mark the page as a user followed link.  This is done so that history can
  // distinguish automatic embed visits from user activated ones.  For example
  // pages loaded in frames are embed visits and lost with the session, while
  // visits across frames should be preserved.
  try {
    if (!PrivateBrowsingUtils.isWindowPrivate(window))
      PlacesUIUtils.markPageAsFollowedLink(href);
  } catch (ex) { /* Skip invalid URIs. */ }
}

/**
 * Handles clicks on links.
 *
 * @return true if the click event was handled, false otherwise.
 */
function handleLinkClick(event, href, linkNode) {
  if (event.button == 2) // right click
    return false;

  var where = whereToOpenLink(event);
  if (where == "current")
    return false;

  var doc = event.target.ownerDocument;

  if (where == "save") {
    saveURL(href, linkNode ? gatherTextUnder(linkNode) : "", null, true,
            true, doc.documentURIObject, doc);
    event.preventDefault();
    return true;
  }

(2) browser\base\content\utilityOverlay.js(119)

/* whereToOpenLink() looks at an event to decide where to open a link.
 *
 * The event may be a mouse event (click, double-click, middle-click) or keypress event (enter).
 *
 * On Windows, the modifiers are:
 * Ctrl        new tab, selected
 * Shift       new window
 * Ctrl+Shift  new tab, in background
 * Alt         save
 *
 * Middle-clicking is the same as Ctrl+clicking (it opens a new tab).
 *
 * Exceptions:
 * - Alt is ignored for menu items selected using the keyboard so you don't accidentally save stuff.  
 *    (Currently, the Alt isn't sent here at all for menu items, but that will change in bug 126189.)
 * - Alt is hard to use in context menus, because pressing Alt closes the menu.
 * - Alt can't be used on the bookmarks toolbar because Alt is used for "treat this as something draggable".
 * - The button is ignored for the middle-click-paste-URL feature, since it's always a middle-click.
 */
function whereToOpenLink( e, ignoreButton, ignoreAlt )
{
  // This method must treat a null event like a left click without modifier keys (i.e.
  // e = { shiftKey:false, ctrlKey:false, metaKey:false, altKey:false, button:0 })
  // for compatibility purposes.
  if (!e)
    return "current";

  var shift = e.shiftKey;
  var ctrl =  e.ctrlKey;
  var meta =  e.metaKey;
  var alt  =  e.altKey && !ignoreAlt;

  // ignoreButton allows "middle-click paste" to use function without always opening in a new window.
  var middle = !ignoreButton && e.button == 1;
  var middleUsesTabs = getBoolPref("browser.tabs.opentabfor.middleclick", true);

  // Don't do anything special with right-mouse clicks.  They're probably clicks on context menu items.

#ifdef XP_MACOSX
  if (meta || (middle && middleUsesTabs))
#else
  if (ctrl || (middle && middleUsesTabs))
#endif
    return shift ? "tabshifted" : "tab";

  if (alt && getBoolPref("browser.altClickSave", false))
    return "save";

  if (shift || (middle && !middleUsesTabs))
    return "window";

  return "current";
}

从源代码可以看出，按住CTRL点击书签，或者用鼠标中键点击书签（与配置相关），都是新标签页打开链接。