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When one Firefox instance finishes starting up it releases the startup lock and deletes the lock directory. Other instances that are waiting to startup are in the meantime polling to acquire the lock but with the directory gone their next attempt just throws a failure and so they assume they don't have the lock yet and keep polling until they hit the five second timeout. With this patch before each attempt to acquire the lock we make sure that the lock directory exists first. Differential Revision: https://phabricator.services.mozilla.com/D161075