"Backfill" is not effective for TV because the particular test does not get run. [Looks like](https://searchfox.org/mozilla-central/rev/f76d80e486028313488d05f4e7fe2509cec11777/toolkit/mozapps/extensions/internal/XPIProvider.jsm#3103) extensions.databaseSchema is meant to change soon after startup or [maybe later](https://searchfox.org/mozilla-central/rev/f76d80e486028313488d05f4e7fe2509cec11777/toolkit/mozapps/extensions/internal/XPIDatabase.jsm#1796). Could the timing be different with the recent conversion to ES modules? Seems like a candidate for [ignorePrefs](https://hg.mozilla.org/mozilla-central/rev/df7eaa7f8d07a127848eb2d7dbaefc3a6c86d2a3#l7.52)? https://searchfox.org/mozilla-central/source/testing/mochitest/ignorePrefs.json
Bug 1838233 Comment 2 Edit History
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["Backfill" is not effective for TV](https://bugzilla.mozilla.org/show_bug.cgi?id=1473661) because the particular test does not get run. [Looks like](https://searchfox.org/mozilla-central/rev/f76d80e486028313488d05f4e7fe2509cec11777/toolkit/mozapps/extensions/internal/XPIProvider.jsm#3103) extensions.databaseSchema is meant to change soon after startup or [maybe later](https://searchfox.org/mozilla-central/rev/f76d80e486028313488d05f4e7fe2509cec11777/toolkit/mozapps/extensions/internal/XPIDatabase.jsm#1796). Could the timing be different with the recent conversion to ES modules? Seems like a candidate for [ignorePrefs](https://hg.mozilla.org/mozilla-central/rev/df7eaa7f8d07a127848eb2d7dbaefc3a6c86d2a3#l7.52)? https://searchfox.org/mozilla-central/source/testing/mochitest/ignorePrefs.json