40137: Built-in https-everywhere storage is not migrated to idb
Fixes #40137 (closed).
One of the problems was
ExtensionStorageIDB.setMigratedExtensionPref being called when the "new"
https-everywhere-eff was installed, which prevented the migration. The patch makes the
https-everywhere-eff extension install/uninstall behave as if the prefs
extensions.webextensions.keepUuidOnUninstall were set to
true, which should allow the migration to be executed correctly when we switch to 10.5.