I flipped the pref: gfx.direct2d.force-enabled;true and it makes firefox believe it can use the D3D10 path and reports a Direct3D10 accelerated window when paired with turning on the hardware acceleration option (layers.accelerate-all;true). I also updated the latest Nvidia drivers. Adapter Description NVIDIA GeForce 7050 / NVIDIA nForce 610i Vendor ID 10de Device ID 07e3 Adapter RAM 256 Adapter Drivers nvd3dum Driver Version 8.17.12.6099 Driver Date 10-16-2010 Direct2D Enabled true DirectWrite Enabled true GPU Accelerated Windows 1/1 Direct3D 10

This is kind of a weird bug. If I leave gfx.direct2d.force-enabled set to false, then it will only report a D3D9 device no matter if I set layers.prefer-D3D9 to true or false.

This is correct behavior. In order for Direct3D 10 layers to be used a Direct3D 10 device needs to be available from Direct2D. This is the case when Direct2D is force-enabled. When Direct2D is not enabled it can never use Direct3D 10 layers. Direct3D 10 layers are the preferred layers type when using Direct2D. Direct3D 9 layers with Direct2D will most likely be removed at some point in the future.