https://news.ycombinator.com/from?site=twitter.com/foone
https://news.ycombinator.com/from?site=github.com/simonw
I find this a great feature for keeping track of individual sources.
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You can still use the domain without the username to see all submissions:
https://news.ycombinator.com/from?site=twitter.com
https://news.ycombinator.com/from?site=github.com