Back in September we announced Firefox had passed the 400 Million Downloads mark. CyberNet had estimated (see below) the 500 Million Downloads mark would be around April 15th. Today (February 22nd) Firefox surpassed the 500 Million Downloads mark! So, when should we expect to see 600 Million Downloads? The estimate is July 30th which is about 5 months and 1 week from today. The Firefox Download* Time Line: November 9, 2004 – Fx 1.0 Released February 16, 2005 – 25 Million Downloads April 29, 2005 – 50 Million Downloads November 2, 2005 – 100 Million Downloads November 29, 2005 –…