Theme for what though?
I will try make an extension for firefox
@anon74637124 look at this
https://addons.mozilla.org/en-US/firefox/search/?platform=windows&q=windows+xp
also this one Search results for "internet explorer" – Add-ons for Firefox (en-US)
for Pale Moon exist look like Netscape theme - Moonscape Link: Pale Moon Add-ons - Moonscape