Complex sentence: The second major milestone (after version 1.0) in Epiphany development was the 2.14 release: this was the first Epiphany release which followed GNOME's version numbering.
Split into simpler sentences: The second major milestone (after version 1.0) in Epiphany development was the 2.14 release. This was the first Epiphany release which followed GNOME's version numbering.