It's used to cache the document body that is eventually passed to SessionHistory.collectFromParent(), and used here. For the content-history case, we use the content document body, but here we're passing the body of the browser element, which is wrong.

We'll probably have to make it possible for the parent to know if the content body has child nodes.

Note that the patches for bug 1700963 will remove this property from the listener, and stop passing a body parameter to SessionHistory.collectFromParent(). We'll use this bug to correctly add the hasChildNodes() behavior.

Note that this only applies to about:blank documents: https://searchfox.org/mozilla-central/rev/185ab5e4f4e01341e009cd4633d1275ffe4d4c8b/toolkit/modules/sessionstore/SessionHistory.jsm#155.

Only applies to non-blank about:blank documents, so this can be pushed out of M7a.

Nika says this bug probably doesn't need to block Fission MVP since it is a corner case that hasn't been a problem yet. Tentatively moving from Fission Milestone MVP to Future.

If you disagree, just let me know or reset the Fission Milestone back to MVP.

Agreed that this can be Fission:Future.

Clearing assignee because Kashav is no longer at Mozilla.