xs2k stated that he purchased the new firmware, allegedly called the "Bittersweet Shimmer" from a developer, and he has now leaked images showing off some new features expected for the Windows Phone 8 OS.
The new update will reportedly bring a Driving Mode feature meaning users can mute calls and texts automatically when hooked up to Bluetooth in a car or activating it manually.
An upgrade to multitasking will mean Windows Phone 8 OS users will be able to close apps by tapping a visible 'X' on the screen while in the multitasking window.
Users will also be able to toggle a switch to disable auto rotation.
Windows Phone Central has since reported some additional features from a source unrelated to the xs2k leak.
The additional features are custom sounds for text, voice mail, e-mail, and reminders, restore over wi-fi when you reset your phone, and a huge amount of work on Bluetooth with various vehicles and devices.
Hardware features for the GDR3 are rumoured to bring 1080p screen res. with advanced Qualcomm processors which should sync in with the release of the Nokia Lumia 1520.
According to The Verge, the screenshots and features are all genuine stating, "Microsoft is currently testing the update, which will debut first on the Nokia Lumia 1520 and a HTC Harmony devie, and is expected to start rolling it out to existing devices later this year."