For months users have been after having GLAMOR enabled within the Debian world since the support is required for the recent AMD "GCN" (HD 7000 / 8000 and Rx 200 series) hardware while it's an optional acceleration architecture for older AMD GPUs as well as an alternative to UXA and SNA for Intel graphics.
GLAMOR is the means of achieving 2D X.Org acceleration in a generic manner using the hardware's OpenGL driver as opposed to dedicated, 2D-specific accelerated driver paths. GLAMOR is an independent library (libglamor) while it's been integrated into X.Org Server 1.16 for offering new options and capabilities.
Per this forum thread and Debian bug report, GLAMOR is now enabled within Debian Experimental. Thus the newer AMD hardware can work out-of-the-box, but within the Debian world you still need to install the Radeon firmware blobs for the accelerated support.