It is not possible to disable e10s, see bug 1724089 for details.

So we should remove the browser.tabs.remote.autostart=false setter at https://searchfox.org/mozilla-central/rev/4b49a0dc50104e03ecadd1fd1902b27be6b9c0c8/toolkit/components/extensions/test/xpcshell/head.js#46 (because it does not work!!!), and reduce the number of distinct xpcshell test manifests.

The current list of tests is described at https://searchfox.org/mozilla-central/rev/4b49a0dc50104e03ecadd1fd1902b27be6b9c0c8/toolkit/components/extensions/test/xpcshell/xpcshell.ini#26-36:

• xpcshell-common.ini - included by xpcshell.ini and xpcshell-remote.ini
• xpcshell-common-e10s.ini - included by xpcshell-remote.ini and xpcshell-e10s.ini
• xpcshell-remote.ini --- e10s + OOP extensions = primary target (all desktop)
• xpcshell-content.ini -- included by xpcshell-remote.ini, xpcshell-e10s.ini and xpcshell.ini
• xpcshell-e10s.ini - e10s + in-process extensions = GeckoView (until bug 1535365 is fixed) however it is currently skipped on Android
• xpcshell.ini - "non-e10s" (e10s in practice) + in-process extensions (former target for Fennec) = GeckoView in practice

We should cut the number of test manifests to three:

• xpcshell-common.ini - unchanged
• xpcshell-common-e10s.ini - merge with xpcshell-remote.ini
• xpcshell-remote.ini - unchanged
• xpcshell-content.ini - merge with xpcshell-common.ini
• xpcshell-e10s.ini - delete (there are no other tests other than the inclusions)
• xpcshell.ini - change comment/tags to match reality: e10s + in-process extensions (GeckoView, until bug 1535365)

Besides merging the test manifests, we should also consolidate head.js (as mentioned before), head_e10s.js and head_remote.js, and check whether the skip-if = os == "android" are still needed (bug 1680132).

Hey Geoff, you might be interested in this because of Thunderbird, not sure how far along with e10s you are there.

Fine by me, we're e10s by default.

Actually, I think this would result in us running some tests we didn't previously run. I'll check that they are passing when I have a build again.

Everything seems fine. We were skipping xpcshell-e10s.ini but I changed that and didn't have any failures. (We still need to skip xpcshell-legacy-ep.ini but you didn't mention that so I assume nothing is changing there.) Thanks for checking.