See the screenshot. It should be under the basic info; try scrolling down.

测试发现Firefox 56受到火狐的Bug 1366290影响，有时会检测不到事件。该Bug在火狐57中修复。

原回复：
是否可以复现这个错误？例如按照…顺序打开时会出错。可以到下载页面右侧“用户支持网站”提出详细问题。
注意如果当前选的是第一个页面，就没有左侧，这时它会按照第二个选项进行选择。
还可以试试2.0版本（下载页底部的开发通道），这个版本改变了实现的方式。

It's because Firefox 57+ compatible extensions cannot access Firefox's internal working, so the browser's default selection cannot be prevented. This extension can only fix it afterwards.

I have downloaded Tree Tabs but cannot reproduce the bug.

In Tree Tabs Settings there is also an option "after closing active tab, activate...", which may cause conflict. Could you try setting this to "let browser handle which tab to activate" and see if it works?

If the problem still exists, open an issue here:
https://github.com/jingyu9575/select-after-closing-current/issues/new
Please share your settings and steps to reproduce e.g. this extension's setting order is ..., that option of Tree Tabs is ... , open tabs in this way ... , and when closing tab ..., I expect ... activates but ... activates instead. Thank you!