It was either Mozilla (Netscape, I think) or IE that it didn’t work on for the longest time.

It works everywhere (it’s now specified in https://html.spec.whatwg.org/multipage/nav-history-apis.html...), but it’s brittle. It can break by adding colliding properties to window deliberately or by accidental global leak (… including things like setting in dev tools), by browser defining new globals, by some 'name' attribute conflict.