Agree with Joost that Intel is typically well supported in LInux. I have Skylate (gen6) system which i got fairly soon after they were released and had no issues setting it up using ~amd64. If you want to run amd64 instead you might need to keyword the kernel and X stuff.
On firefox about:support, i have; Multiprocess Windows 1/1 (Enabled by user) and; Features Compositing OpenGL Asynchronous Pan/Zoom wheel input enabled; touch input enabled WebGL Renderer X.Org -- Gallium 0.4 on AMD TONGA (DRM 3.8.0 / 4.9.6-gentoo-r1, LLVM 4.0.0) WebGL2 Renderer X.Org -- Gallium 0.4 on AMD TONGA (DRM 3.8.0 / 4.9.6-gentoo-r1, LLVM 4.0.0) Hardware H264 Decoding No Audio Backend pulse GPU #1 Active Yes Description X.Org -- Gallium 0.4 on AMD TONGA (DRM 3.8.0 / 4.9.6-gentoo-r1, LLVM 4.0.0) Vendor ID X.Org Device ID Gallium 0.4 on AMD TONGA (DRM 3.8.0 / 4.9.6-gentoo-r1, LLVM 4.0.0) Driver Version 3.0 Mesa 17.0.2 Diagnostics AzureCanvasAccelerated 0 AzureCanvasBackend skia AzureContentBackend skia AzureFallbackCanvasBackend none CairoUseXRender 0 Decision Log HW_COMPOSITING blocked by default: Acceleration blocked by platform force_enabled by user: Force-enabled by pref OPENGL_COMPOSITING force_enabled by user: Force-enabled by pref I cant see any references to OMTC, but there are some layers.acceleration.* and layers.offmainthreadcomposition.* configs, but they're all set to the defaults.
