However, following a dispute in March 1997 concerning each other's performance and because of contract negotiations with Bristol to access Windows source code after September 1997 failing, Microsoft reversed course and decided to directly port the Windows version in-house using the MainWin XDE (eXtended Development Environment) application from Mainsoft, the main competitor to Bristol Technology. (Microsoft would later also use MainWin to port Windows Media Player and Outlook Express to Unix.) Now well behind schedule, the 3.0 branch was apparently scrapped in favor of 4.0 (that was released for Windows half a year earlier), which used the new Trident rendering engine. A beta of the Solaris version was made available on November 5, 1997, with a final version expected by March 1998.