This really only matters much in cases where document.domain is involved, I think. But while we have an incumbent global there anyway, why not use it?

I'm pretty sure it's historical, but I'm also pretty sure it should never make an observable difference, modulo consumers that extract a URI from the principal. That is to say, the incumbent should always be same-origin with the subject, since that's how the web works, and also because we enforce it here: http://hg.mozilla.org/mozilla-central/file/tip/dom/base/ScriptSettings.cpp#l151

> modulo consumers that extract a URI from the principal Right. The thing that extracts URIs here is content policies. I think using the incumbent makes a lot more sense here, honestly, for the consumers who do care about the URI.

(In reply to Boris Zbarsky [:bz] from comment #3) > > modulo consumers that extract a URI from the principal > > Right. The thing that extracts URIs here is content policies. > > I think using the incumbent makes a lot more sense here, honestly, for the > consumers who do care about the URI. That is fine with me, sure. Though I really wish we tracked URI and origin separately...