The decision has been made for a long time now and is not going to change now just to support something that a minority may use until EOL in April next year. Firefox 53.0 and later completely dropped support of the EOL WinXP and Vista so no new version is a an option. It was a bonus that the 52 ESR was a option for WinXP and Vista users to still have a browser option for a while longer. It was almost 2 1/2 years past when Chrome, Chromium, Opera dropped XP/Vista back in April 2016 and 4 1/2 years since Microsoft made XP EOL in support for regular users. There was a discussion on this in [/questions/1222390] Also https://chuttenblog.wordpress.com/2018/09/05/the-end-of-firefox-windows-xp-support/