Watermelon Vanadium separates different origins into processes rather than conflating different subdomains of the same TLD into the same process
Should be said that there's a blacklist being maintained of sites that provide hosting of content by third-parties on their subdomains. I think both Firefox and Chromium use it to separate their subdomains into their own processes without conflating into the TLD site process.
https://publicsuffix.org/
https://en.wikipedia.org/wiki/Public_Suffix_List