我看不出这个问题与facebook AJAX有什么关系。事实上，禁用JavaScript和完全基于重定向的登录也会出现这个问题。

一个与facebook交换的例子:

1. GET <https://www.facebook.com/dialog/oauth?client_id=MY_APP_ID&scope=email&redirect_uri=MY_REDIRECT_URL> RESPONSE 302 Found Location: <https://www.facebook.com/connect/uiserver.php?[...]>  
2. GET <https://www.facebook.com/connect/uiserver.php?[...]> RESPONSE 302 Found MY_REDIRECT_URL?code=FB_CODE#_  
3. GET MY_REDIRECT_URL?code=FB_CODE#_  

我也只在火狐浏览器上遇到过这种情况。

通过Facebook平台更新:

更改会话重定向行为 本周，我们开始在redirect_uri中添加一个片段#____=____ 该字段为空。请确保您的应用程序可以处理这个问题 的行为。

为了防止这种情况，在你的登录url请求中设置redirect_uri(使用Facebook php-sdk)

$facebook->getLoginUrl(array('redirect_uri' => $_SERVER['SCRIPT_URI'],'scope' => 'user_about_me'));

更新

上述内容正是文档中所述的修复此问题的方法。然而，Facebook记录的解决方案并不奏效。请考虑在Facebook平台更新博客上留下评论，并关注这个错误以获得更好的答案。在此之前，将以下内容添加到head标签以解决此问题:

<script type="text/javascript">
    if (window.location.hash && window.location.hash == '#_=_') {
        window.location.hash = '';
    }
</script>

或者一个更详细的选择(感谢niftylettuce):

<script type="text/javascript">
    if (window.location.hash && window.location.hash == '#_=_') {
        if (window.history && history.pushState) {
            window.history.pushState("", document.title, window.location.pathname);
        } else {
            // Prevent scrolling by storing the page's current scroll offset
            var scroll = {
                top: document.body.scrollTop,
                left: document.body.scrollLeft
            };
            window.location.hash = '';
            // Restore the scroll offset, should be flicker free
            document.body.scrollTop = scroll.top;
            document.body.scrollLeft = scroll.left;
        }
    }
</script>

使用angular和angular ui router，你可以修复这个问题

    app.config(function ($stateProvider, $urlRouterProvider, $locationProvider) {

      // Make a trailing slash optional for all routes
      // - Note: You'll need to specify all urls with a trailing slash if you use this method.
      $urlRouterProvider.rule(function ($injector, $location) {
        /***
        Angular misbehaves when the URL contains a "#_=_" hash.

        From Facebook:
          Change in Session Redirect Behavior
          This week, we started adding a fragment #_=_ to the redirect_uri when this field is left blank.
          Please ensure that your app can handle this behavior.

        Fix:
          http://stackoverflow.com/questions/7131909/facebook-callback-appends-to-return-url#answer-7297873
        ***/
        if ($location.hash() === '_=_'){
          $location.hash(null);
        }

        var path = $location.url();

        // check to see if the path already has a slash where it should be
        if (path[path.length - 1] === '/' || path.indexOf('/?') > -1) {
          return;
        }
        else if (path.indexOf('?') > -1) {
          $location.replace().path(path.replace('?', '/?'));
        }
        else {
          $location.replace().path(path + '/');
        }
      });

      // etc ...
    });
});

Facebook最近在处理会话重定向的方式上做出了改变。有关公告，请参阅本周Operation Developer Love博客文章中的“会话重定向行为的更改”。

博士TL;

if (window.location.hash === "#_=_"){
    history.replaceState 
        ? history.replaceState(null, null, window.location.href.split("#")[0])
        : window.location.hash = "";
}

完整版本与一步一步的说明

// Test for the ugliness.
if (window.location.hash === "#_=_"){

    // Check if the browser supports history.replaceState.
    if (history.replaceState) {

        // Keep the exact URL up to the hash.
        var cleanHref = window.location.href.split("#")[0];

        // Replace the URL in the address bar without messing with the back button.
        history.replaceState(null, null, cleanHref);

    } else {

        // Well, you're on an old browser, we can get rid of the _=_ but not the #.
        window.location.hash = "";

    }

}

循序渐进:

We'll only get into the code block if the fragment is #_=_. Check if the browser supports the HTML5 window.replaceState method. Clean the URL by splitting on # and taking only the first part. Tell history to replace the current page state with the clean URL. This modifies the current history entry instead of creating a new one. What this means is the back and forward buttons will work just the way you want. ;-) If the browser does not support the awesome HTML 5 history methods then just clean up the URL as best you can by setting the hash to empty string. This is a poor fallback because it still leaves a trailing hash (example.com/#) and also it adds a history entry, so the back button will take you back to #_-_.

了解更多关于历史的知识。

了解window.location的更多信息。

对我来说，我让JavaScript重定向到另一个页面，以摆脱#_=_。下面的想法应该有用。：）

function redirect($url){
    echo "<script>window.location.href='{$url}?{$_SERVER["QUERY_STRING"]}'</script>";        
}