It is not possible to upgrade to a version of Firefox later than 52 on Windows XP. This article has more information: https://blog.mozilla.org/futurereleases/2017/10/04/firefox-support-for-windows-xp-and-vista/ .

If possible, you should upgrade to a newer operating system.

That article has some misinformation as the Firefox 52 ESR will actually be supported on WinXP/Vista until 52.8.0 ESR in May 2018.

The September 2017 comment was gong by the outdated comment in https://support.mozilla.org/en-US/kb/end-support-windows-xp-and-vista as current version of article has not been updated since Dec 2016.

Download the web-browser here. It is a little ahead of your current one. Get Linux or upgrade your version of Windows and probably your computer. Windows 10 spies on you and it cannot be stopped, it can be slowed down at this time and keeps being turned on again by Microsoft and the 3rd party's they deal with. Windows 7 and Windows 8/8.1 are being turned into Windows 10. Apple Mac's are not as bad, but do the same thing. Google software and hardware does the same thing. Linux has a large learning curve and you need to learn about a few security things to install.

https://www.mozilla.org/en-US/firefox/new

This should be the file as of today's date: Firefox Setup 52.5.0esr.exe

James a Moderator in another thread posted this: The better link to use for current Release of Firefox 52 ESR is https://www.mozilla.org/firefox/organizations/all/