Now that this has shipped, we should consider removing these preferences to reduce our ongoing maintenance cost:

• browser.tabs.remote.useCrossOriginOpenerPolicy
• browser.tabs.remote.useCrossOriginEmbedderPolicy
• dom.postMessage.sharedArrayBuffer.withCOOP_COEP

Note that we should not touch javascript.options.shared_memory.

These preferences are still set to false on Android by default due to DocumentChannel.

Although https://bugzilla.mozilla.org/show_bug.cgi?id=1589982 hasn't been solved yet, the pref for Document Channel has been set to true in https://bugzilla.mozilla.org/show_bug.cgi?id=1617189

I guess the quickest/easiest way to figure out if we can safely remove them is to see whether we will have new test failures on try after setting these prefs to true on Android: https://treeherder.mozilla.org/#/jobs?repo=try&revision=19f28988865e219b2bc78ac918683ca83231d26a

Thanks Tom, not sure how I forgot about that. We also need bug 1530770 and that looks unfinished still. Let's wait for Android support and revisit this bug then.