After speaking with mattwoodrow and kmag we decided we can begin deprecating browser.tabs.remote.allowLinkedWebInFileUriProcess by ignoring it when documentChannel is enabled. We currently ignore it when fission is enabled already.

This bug is important for security, but it doesn't need to block Fission dogfooding (M5).

https://hg.mozilla.org/mozilla-central/rev/b158903288bb

Should we consider backing this out given all the regressions? At least we should get the regressions fixed on beta.

Firefox 76 releases next week and already has some of the fixes. If we did a backout I'd say we'd want to do it for that so that 76 fixed everything, but that'd also mean backing out the fixes while we upload further fixes to 77 which'll be in beta by then.

All the regressions have to do with file:// content linking to http(s):// content. The impact seems low to me since I hardly ever use file:// URLs, but multiplied by all our release channel user base...

NI: Julien, I feel I don't really have the info to make this call.

I started working on fixes for the specific regressions, but I think the better choice would be to make a patch that effectively backs out the problematic changes, but that also doesn't need to undo the patches I've made since. I'll do that tomorrow since it's already getting late now.

(In reply to Paul Bone [:pbone] from comment #7)

I started working on fixes for the specific regressions, but I think the better choice would be to make a patch that effectively backs out the problematic changes, but that also doesn't need to undo the patches I've made since. I'll do that tomorrow since it's already getting late now.

I filed new bug 1634779 to track the review and landing of backout patch in Fx76 (separately from this closed bug that just flipped the pref off).

It's too late for 76 at this point.