OK, just checked with UX/PM on Slack and they confirmed that we do want to fully delete the last profile (but I'm not clear on whether this decision was documented anywhere). In this case the idea is to restart Firefox with a totally fresh profile, so I think we'd want to schedule background deletion of the last profile, but also remove its Profile entry from profiles.ini, as well as the default path for the Install, so that on restart, we would go through the toolkit first run profile creation flow.
Bug 1927925 Comment 0 Edit History
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Following on the 10/30 discussion, we want to delete the last profile by creating a new profile in the group, scheduling deletion of the current profile, then restarting into the new profile, so that users continue to have the profiles feature available but it is clear to them that the data from that last profile has been removed