I have been testing other browsers for modern website compatibility on XP. The only ones besides the 3 above that are still maintained at the time of this writing are K-Meleon, QT-Web and derivitaves (Otter) and Advanced Chrome 54.20.6530.0. so I downloaded and installed. There are other browsers rumored to be working on XP (Yandex) but their websites are scant on system requirements and wanted me to "Agree to participate in improving Yandex services by sending browser usage statistics to the developers". Hard pass on Yandex for my testing.
I put them though their paces and ran into a few glitches (QTWeb/Otter are crash-prone). For example, ESPN.COM wouldn't show the high scores banners on those web browsers. Another site I visit regularly, Masslive.com, doesn't render properly on any of these browsers
Here's the site on NewMoon/MyPal, Serpent/Basilisk AND any current version of Chrome/Firefox on newer Windows:
NewMoon/MyPal and Serpent/Basilisk are still the champs on Windows XP. The other browsers I tested worked fine with most websites but as you can see had some quirks with CSS rendering on certain sites.
Please note I am not in denial about XP's end of life, I could easily install a Linux distro on this old laptop but for now I'll keep XP for the sake of nostalgia. At least modern websites are still accessible (I also went on Discord's test server, worked fine). My next test is Skype's web client - will post follow-up when I get a chance to test.
In the meantime I would like to hear anyone else's experiences with other browsers still being maintained for XP, specifically I am interested in an updated Chromium based browser for XP - Advanced Chrome Custom is based on Chromium 54 and that still had rendering issues on certain sites. Try ESPN and Masslive.com for baseline.