Good afternoon, try making these settings that improve XP performance.
Look at these links.
http://informaticaxp.net/acelera-tu-conexion-a-internet-modificando-el-registro-de-windows https://support.microsoft.com/es-es/help/15055/windows-7-optimize -windows-better-performance
While this link is for Windows 7, it is also applicable for Windows XP. Disable all unused software that does not load all at once, only when you use it. To see what Windows and the programs do, you have to open the (task manager). Press the keys: Windows + R, to run, type msconfig
https://www.google.es/amp/s/lecciones.batiburrillo.net/habilitar-el-administrador-de-tareas-de-windows-xp/amp/
And finally, when you are in the Windows task manager select the one that corresponds to the browser you are using, press the right mouse button and give "high" priority this makes Windows give more hardware resources to the selected software.
I found these browsers compatible with XP.
Pale Moon, the alternative to Firefox still compatible with Vista (and with a special version for Windows XP).
https://www.palemoon.org/#
Qt Web Browser, a browser compatible even with Windows 2000.
http://www.qtweb.net/
SlimBrowser, a fast, efficient and safe alternative.
http://www.slimbrowser.net/es/
You try these browsers and see which one is more efficient, remember that if you want the browser or any other program to work faster with high priority, it makes it work faster.

Regards, David