Windows Phone 7.8 is a certainty; it will land early 2013, according to Microsoft, for those who have certain legacy Windows Phone 7 devices, to bridge the gap between version-seven-phones and version-eight-devices. A recent Nokia survey shed some light on what both Microsoft and the manufacturer will include but we’re now seeing some ROMs on Navifirm.
Windows Phone 7.8 (with builds 8858.12560) has popped up on online and it looks like the targeted phones are the Lumia 800 and Lumia 510 (which was the first phone caught on camera running 7.8). According to reports the new version of the firmware brings resizable Live Tiles as expected, Bluetooth sharing, a new Store icon, the Ringtone Maker app, Lock Screen wallpapers from Bing, added Accent colors, Xbox and Office icons, a new boot screen, and some more.
Update: As SteZay points out in the comments below, the Windows Phone 7.8 ROM for the Lumia 900 RM-823 is also there.