--- a/dom/canvas/WebGLFormats.cpp
+++ b/dom/canvas/WebGLFormats.cpp
@@ -1,15 +1,16 @@
 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "WebGLFormats.h"
 
+#include "gfxPrefs.h"
 #include "GLDefs.h"
 #include "mozilla/StaticMutex.h"
 
 #ifdef FOO
 #error FOO is already defined! We use FOO() macros to keep things succinct in this file.
 #endif
 
 namespace mozilla {
@@ -801,16 +802,23 @@ FormatUsageAuthority::CreateForWebGL2(gl
     fnAddSizedUnpack(FOO(DEPTH_COMPONENT16 ), LOCAL_GL_DEPTH_COMPONENT, LOCAL_GL_UNSIGNED_INT  );
     fnAddSizedUnpack(FOO(DEPTH_COMPONENT24 ), LOCAL_GL_DEPTH_COMPONENT, LOCAL_GL_UNSIGNED_INT  );
     fnAddSizedUnpack(FOO(DEPTH_COMPONENT32F), LOCAL_GL_DEPTH_COMPONENT, LOCAL_GL_FLOAT         );
 
     // DEPTH_STENCIL
     fnAddSizedUnpack(FOO(DEPTH24_STENCIL8 ), LOCAL_GL_DEPTH_STENCIL, LOCAL_GL_UNSIGNED_INT_24_8             );
     fnAddSizedUnpack(FOO(DEPTH32F_STENCIL8), LOCAL_GL_DEPTH_STENCIL, LOCAL_GL_FLOAT_32_UNSIGNED_INT_24_8_REV);
 
+    if (gfxPrefs::WebGL2CompatMode()) {
+        AddSimpleUnsized(ptr, LOCAL_GL_RGBA, LOCAL_GL_FLOAT, EffectiveFormat::RGBA32F);
+        AddSimpleUnsized(ptr, LOCAL_GL_RGB , LOCAL_GL_FLOAT, EffectiveFormat::RGB32F );
+
+        AddSimpleUnsized(ptr, LOCAL_GL_RGBA, LOCAL_GL_HALF_FLOAT_OES, EffectiveFormat::RGBA16F);
+        AddSimpleUnsized(ptr, LOCAL_GL_RGB , LOCAL_GL_HALF_FLOAT_OES, EffectiveFormat::RGB16F );
+    }
 #undef FOO
 
     SetUsage(ptr, EffectiveFormat::Luminance8Alpha8, false, true);
     SetUsage(ptr, EffectiveFormat::Luminance8      , false, true);
     SetUsage(ptr, EffectiveFormat::Alpha8          , false, true);
 
     AddBasicUnsizedFormats(ptr, gl);
 

--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -425,16 +425,18 @@ private:
   DECL_GFX_PREF(Once, "webgl.force-layers-readback",           WebGLForceLayersReadback, bool, false);
   DECL_GFX_PREF(Live, "webgl.lose-context-on-memory-pressure", WebGLLoseContextOnMemoryPressure, bool, false);
   DECL_GFX_PREF(Live, "webgl.max-warnings-per-context",        WebGLMaxWarningsPerContext, uint32_t, 32);
   DECL_GFX_PREF(Live, "webgl.min_capability_mode",             WebGLMinCapabilityMode, bool, false);
   DECL_GFX_PREF(Live, "webgl.msaa-force",                      WebGLForceMSAA, bool, false);
   DECL_GFX_PREF(Live, "webgl.prefer-16bpp",                    WebGLPrefer16bpp, bool, false);
   DECL_GFX_PREF(Live, "webgl.restore-context-when-visible",    WebGLRestoreWhenVisible, bool, true);
 
+  DECL_GFX_PREF(Live, "webgl.webgl2-compat-mode",              WebGL2CompatMode, bool, false);
+
   // WARNING:
   // Please make sure that you've added your new preference to the list above in alphabetical order.
   // Please do not just append it to the end of the list.
 
 public:
   // Manage the singleton:
   static gfxPrefs& GetSingleton()
   {

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -4199,16 +4199,17 @@ pref("webgl.can-lose-context-in-foregrou
 pref("webgl.restore-context-when-visible", true);
 pref("webgl.max-warnings-per-context", 32);
 pref("webgl.enable-draft-extensions", false);
 pref("webgl.enable-privileged-extensions", false);
 pref("webgl.bypass-shader-validation", false);
 pref("webgl.enable-prototype-webgl2", false);
 pref("webgl.disable-fail-if-major-performance-caveat", false);
 pref("webgl.disable-DOM-blit-uploads", false);
+pref("webgl.webgl2-compat-mode", false);
 
 #ifdef RELEASE_BUILD
 // Keep this disabled on Release and Beta for now. (see bug 1171228)
 pref("webgl.enable-debug-renderer-info", false);
 #else
 pref("webgl.enable-debug-renderer-info", true);
 #endif