The oldest instance of it that I know is putting something like download before or after the youtube domain. This must have been 2008±2. I very much doubt that's the first instance ever but I wasn't around online in the 90s (aside from on my grandma's machine who didn't know her computer had a web browser, but that wasn't very conscious, just a neutral net (young me) clicking buttons to see the effect)

It works well with bookmarklets. This swizzles between arxiv.org <-> www.talk2arxiv.org. I've now added it to my Favorites bar, next to arxiv.org/abs <-> arxiv.org/pdf and twitter.org <-> nitter.net. Thanks for the service!

javascript:((u,a,b,c)=%3Ewindow.location.href=u.match(a)?u.replace(a,b):u.startsWith(b)?u.replace(b,c):u)(window.location.href,/https:\/\/arxiv\.org\/(abs|pdf)\//,'https://www.talk2arxiv.org/pdf/','https://arxiv.org/pdf/')

It bugs me cause it's kinda true but kinda misleading, I don't know if casual web users realize it's a whole different domain. Sometimes it's not important, sometimes it is.

I use this on mitta.us/ to save pages. Got the idea from saved.io/, which does something similar.

CERN circa 1994.

nyud.net (coral cdn) was my first experience with this pattern... back from the slashdot days in the 00s.