If I set my firewall to block all traffic but HTTP/HTTPS then proceed to launch Firefox, Firefox will delay ten to fifteen seconds before launching. In my experience with other programs, such a delay usually means the software is trying to connect to a server somewhere and is timing out once it determines that it cannot connect. I guessed that perhaps it might be Firefox searching for updates or reporting data (telemetry, health & crash data) but I disabled the update check and the data-reporting and the delay is still present. What is likely causing this delay?

Windows XP Firefox 35.0 Delay occurs even when using a clean profile (default settings and no plugins installed).