If SeaMonkey or Thunderbird needs to restart for an EM-initiated reason, such as installing an extension, then the offline startup prompt happens twice, once on the original launch and once on the restart. This is because it prompts on the profile-after-change notification, which happens in the EM restart case. We may want to switch to a later notification, such as final-ui-startup. I don't know whether the profile-change-net-teardown notification happens in the EM restart case. We may not want to add the observer until final ui startup.
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