In bug 1732473 I added test coverage to verify that the cookies API behaves sensibly for erroneous situations.

The patch got backed out because of failures on Android, at https://hg.mozilla.org/integration/autoland/rev/ee872b2362bb#l1.91

TEST-UNEXPECTED-FAIL | xpcshell.ini:toolkit/components/extensions/test/xpcshell/test_ext_cookies_errors.js | test_error_messages - [test_error_messages : 181] Promise rejected, expecting rejection to match "Invalid cookie store id: \"firefox-container-99\"", got "Permission denied to set cookie

The failure is caused by the fact that on Android, the cookieStoreId parser doesn't actually check the validity of the cookieStoreId:
https://searchfox.org/mozilla-central/rev/4c184ca81b28f1ccffbfd08f465709b95bcb4aa1/toolkit/components/extensions/parent/ext-toolkit.js#88-90
Fixing that depends on bug 1643740.

The test file introduced in bug 1470651, i.e. toolkit/components/extensions/test/xpcshell/test_ext_contentScripts_register.js,
should also be updated once the parent bug (bug 1643740) gets fixed.