插件的安装文件名为flagfox-5.2.3-fx+sm.xpi。

插件下载地址：https://github.com/attawjy/Firefox-old-addons-collection/blob/master/flagfox-5.2.3-fx%2Bsm.xpi

官网介绍：
https://flagfox.net/viewtopic.php?t=552

Flagfox 5.2.3 was the last standard version of Flagfox to support versions of Firefox prior to Firefox 57, due to a mandatory rewrite to use Mozilla/Google's new WebExtension API, after which point Mozilla banned all prior "legacy" APIs and banned addons that used them from posting any updates, as of the Firefox 57 release. Everyone should use Flagfox 6.0+ if it is supported by your browser version. Flagfox 5.2.x is currently the only version of Flagfox to support Firefox 52 ESR or SeaMonkey (which is currently based on 52 ESR), as WebExtension support is insufficient in those versions. Firefox 52 ESR will receive security/stability updates until mid-2018, after which point you'll need to upgrade or be unsafe, regardless of whether you like their new versions or not. Flagfox 5.2.4 and potential future updates exist to continue support for Firefox 52 ESR, which Mozilla doesn't really fully support, but is still in wide use. Updates will not be released every month and will not be released indefinitely.

Use of particularly old versions of Flagfox will eventually result in inaccurate flags, as your IP location database will be out of date.

这个版本的缺点是IP地址库很旧，像Purasbar这样的新网站就没有任何数据。