This is a difference between what's called "transitional" and "nontransitional" IDNA processing. The WHATWG URL standard mandates nontransitional processing, w

This is a difference between what's called "transitional" and "nontransitional" IDNA processing. The WHATWG URL standard mandates nontransitional processing, which says meßagefactory.ca becomes xn--meagefactory-m9a.ca. Firefox and Safari follow the standard. Chrome and Edge are still using transitional processing. Here's the Chrome bug to switch to nontransitional processing (which appears to be very close to shipping): https://bugs.chromium.org/p/chromium/issues/detail?id=694157 https://bugs.chromium.org/p/chromium/issues/detail?id=694157 In 2021, Go's HTTP client switched from transitional to nontransitional processing and the relevant issue is quite informative: https://github.com/golang/go/issues/46001 https://github.com/golang/go/issues/46001