In order to support isolated mozbrowsers in Fission, most of the docshell logic they're built on would have to be moved to BrowsingContext. Since isolated mozbrowsers seem to be unused and unwanted at this point, though, we're better off just removing support.

Are you planning to remove the associated origin attribute as well?

(In reply to :Ehsan Akhgari from comment #1)

Are you planning to remove the associated origin attribute as well?

Yes

This functionality is currently unused, and blocks work needed to support
Fission.

https://hg.mozilla.org/mozilla-central/rev/2bdc5f8ac30e
https://hg.mozilla.org/mozilla-central/rev/065a5198a0dc

Roll some unfixed bugs from Fission Milestone M4 to M5

0ee3c76a-bc79-4eb2-8d12-05dc0b68e732

M6

The leave-open keyword is there and there is no activity for 6 months.
:kmag, maybe it's time to close this bug?

This bug is a Fission Nightly blocker (milestone M6b).

kmag says he will confirm he has all the patch reviewers needed.

kmag said all the fission-blocking work is complete here and the remaining do not block Fission.

The leave-open keyword is there and there is no activity for 6 months.
:jstutte, maybe it's time to close this bug?

The leave-open keyword is there and there is no activity for 6 months.
:jstutte, maybe it's time to close this bug?

The leave-open keyword is there and there is no activity for 6 months.
:hsinyi, maybe it's time to close this bug?

The leave-open keyword is there and there is no activity for 6 months.
:kmag, maybe it's time to close this bug?
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