Complex sentence: Firefox 2 began to lose notable market share to Firefox 3 within 24 hours after its release, Firefox 3 usage rose from under 1% to over 3% according to Net Applications in that time period.
Split into simpler sentences: Firefox 2 began to lose notable market share to Firefox 3. Within 24 hours after its release, Firefox 3 usage rose from under 1% to over 3% according to Net Applications in that time period.