--- a/dom/canvas/WebGLContext.cpp
+++ b/dom/canvas/WebGLContext.cpp
@@ -598,18 +598,25 @@ WebGLContext::CreateAndInitGL(bool force
     // --
 
     typedef decltype(gl::GLContextProviderEGL::CreateOffscreen) fnCreateOffscreenT;
     const auto fnCreate = [&](fnCreateOffscreenT* const pfnCreateOffscreen,
                               const char* const info)
     {
         const gfx::IntSize dummySize(1, 1);
         nsCString failureId;
-        const RefPtr<GLContext> gl = pfnCreateOffscreen(dummySize, surfaceCaps, flags,
-                                                        &failureId);
+        RefPtr<GLContext> gl = pfnCreateOffscreen(dummySize, surfaceCaps, flags,
+                                                  &failureId);
+        if (gl && gl->IsCoreProfile() &&
+            !(flags & gl::CreateContextFlags::REQUIRE_COMPAT_PROFILE) &&
+            !gl->IsSupported(gl::GLFeature::gpu_shader5))
+        {
+            const auto compatFlags = flags | gl::CreateContextFlags::REQUIRE_COMPAT_PROFILE;
+            gl = pfnCreateOffscreen(dummySize, surfaceCaps, compatFlags, &failureId);
+        }
         if (!gl) {
             out_failReasons->push_back(WebGLContext::FailureReason(failureId, info));
         }
         return gl;
     };
 
     const auto newGL = [&]() -> RefPtr<gl::GLContext> {
         if (tryNativeGL) {

--- a/dom/canvas/WebGLShaderValidator.cpp
+++ b/dom/canvas/WebGLShaderValidator.cpp
@@ -1,15 +1,16 @@
 /* -*- Mode: C++; tab-width: 20; 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 "WebGLShaderValidator.h"
 
+#include <algorithm>
 #include "gfxPrefs.h"
 #include "GLContext.h"
 #include "mozilla/gfx/Logging.h"
 #include "mozilla/Preferences.h"
 #include "MurmurHash3.h"
 #include "nsPrintfCString.h"
 #include <string>
 #include <vector>
@@ -96,22 +97,31 @@ ChooseValidatorCompileOptions(const ShBu
     return options;
 }
 
 } // namespace webgl
 
 ////////////////////////////////////////
 
 static ShShaderOutput
-ShaderOutput(gl::GLContext* gl)
+ShaderOutput(gl::GLContext* const gl)
 {
     if (gl->IsGLES()) {
         return SH_ESSL_OUTPUT;
     } else {
         uint32_t version = gl->ShadingLanguageVersion();
+
+        // Version 130 starts to require integral constant expressions for loop indices.
+        // Both version 400 and gpu_shader5 remove this restrictions.
+        // gpu_shader5 went core in 400, so we can just check for the GLFeature.
+        // If we're compiling for webglsl1, even for webgl2, we need gpu_shader5, or GLSL_COMPAT.
+        if (!gl->IsSupported(gl::GLFeature::gpu_shader5)) {
+            version = std::min<uint32_t>(version, 120);
+        }
+
         switch (version) {
         case 100: return SH_GLSL_COMPATIBILITY_OUTPUT;
         case 120: return SH_GLSL_COMPATIBILITY_OUTPUT;
         case 130: return SH_GLSL_130_OUTPUT;
         case 140: return SH_GLSL_140_OUTPUT;
         case 150: return SH_GLSL_150_CORE_OUTPUT;
         case 330: return SH_GLSL_330_CORE_OUTPUT;
         case 400: return SH_GLSL_400_CORE_OUTPUT;

--- a/dom/canvas/test/webgl-conf/generated-mochitest.ini
+++ b/dom/canvas/test/webgl-conf/generated-mochitest.ini
@@ -11031,17 +11031,16 @@ subsuite = webgl1-ext
 subsuite = webgl1-ext
 skip-if = (os == 'android')
 [generated/test_conformance__glsl__bugs__qualcomm-loop-with-continue-crash.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__bugs__sampler-array-struct-function-arg.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__bugs__sampler-array-using-loop-index.html]
 subsuite = webgl1-ext
-fail-if = (os == 'linux')
 [generated/test_conformance__glsl__bugs__sampler-struct-function-arg.html]
 subsuite = webgl1-ext
 skip-if = (os == 'linux') || (os == 'android')
 [generated/test_conformance__glsl__bugs__sequence-operator-evaluation-order.html]
 subsuite = webgl1-ext
 skip-if = (os == 'android')
 [generated/test_conformance__glsl__bugs__sketchfab-lighting-shader-crash.html]
 subsuite = webgl1-ext
@@ -11503,16 +11502,17 @@ subsuite = webgl1-ext
 [generated/test_conformance__glsl__misc__shader-with-while-loop.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__misc__shader-without-precision.frag.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__misc__shaders-with-constant-expression-loop-conditions.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__misc__shaders-with-invariance.html]
 subsuite = webgl1-ext
+fail-if = (os == 'linux')
 [generated/test_conformance__glsl__misc__shaders-with-mis-matching-uniforms.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__misc__shaders-with-mis-matching-varyings.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__misc__shaders-with-missing-varyings.html]
 subsuite = webgl1-ext
 [generated/test_conformance__glsl__misc__shaders-with-name-conflicts.html]
 subsuite = webgl1-ext

--- a/dom/canvas/test/webgl-conf/mochitest-errata.ini
+++ b/dom/canvas/test/webgl-conf/mochitest-errata.ini
@@ -183,19 +183,17 @@ skip-if = (os == 'linux') || (os == 'mac
 [generated/test_conformance__glsl__constructors__glsl-construct-ivec4.html]
 # Assume crashes like ivec3
 skip-if = (os == 'linux') || (os == 'mac')
 
 [generated/test_conformance__glsl__constructors__glsl-construct-mat2.html]
 # Crashes on Linux ASAN
 skip-if = ((os == 'linux') && asan)
 
-[generated/test_conformance__glsl__bugs__sampler-array-using-loop-index.html]
-# Testfail on Linux after removing SH_UNROLL_FOR_LOOP_WITH_SAMPLER_ARRAY_INDEX.
-# Only happen on tryserver
+[generated/test_conformance__glsl__misc__shaders-with-invariance.html]
 fail-if = (os == 'linux')
 
 [generated/test_conformance__misc__type-conversion-test.html]
 fail-if = (os == 'linux')
 # Resets device on Android 2.3.
 # Crashes on desktop Linux.
 skip-if = (os == 'android') || (os == 'linux')
 

--- a/gfx/gl/GLContext.cpp
+++ b/gfx/gl/GLContext.cpp
@@ -91,16 +91,17 @@ static const char* const sExtensionNames
     "GL_ARB_compatibility",
     "GL_ARB_copy_buffer",
     "GL_ARB_depth_texture",
     "GL_ARB_draw_buffers",
     "GL_ARB_draw_instanced",
     "GL_ARB_framebuffer_object",
     "GL_ARB_framebuffer_sRGB",
     "GL_ARB_geometry_shader4",
+    "GL_ARB_gpu_shader5",
     "GL_ARB_half_float_pixel",
     "GL_ARB_instanced_arrays",
     "GL_ARB_internalformat_query",
     "GL_ARB_invalidate_subdata",
     "GL_ARB_map_buffer_range",
     "GL_ARB_occlusion_query2",
     "GL_ARB_pixel_buffer_object",
     "GL_ARB_robust_buffer_access_behavior",
@@ -131,16 +132,17 @@ static const char* const sExtensionNames
     "GL_EXT_draw_instanced",
     "GL_EXT_draw_range_elements",
     "GL_EXT_frag_depth",
     "GL_EXT_framebuffer_blit",
     "GL_EXT_framebuffer_multisample",
     "GL_EXT_framebuffer_object",
     "GL_EXT_framebuffer_sRGB",
     "GL_EXT_gpu_shader4",
+    "GL_EXT_gpu_shader5",
     "GL_EXT_multisampled_render_to_texture",
     "GL_EXT_occlusion_query_boolean",
     "GL_EXT_packed_depth_stencil",
     "GL_EXT_read_format_bgra",
     "GL_EXT_robustness",
     "GL_EXT_sRGB",
     "GL_EXT_sRGB_write_control",
     "GL_EXT_shader_texture_lod",
@@ -162,16 +164,17 @@ static const char* const sExtensionNames
     "GL_KHR_robust_buffer_access_behavior",
     "GL_KHR_robustness",
     "GL_KHR_texture_compression_astc_hdr",
     "GL_KHR_texture_compression_astc_ldr",
     "GL_NV_draw_instanced",
     "GL_NV_fence",
     "GL_NV_framebuffer_blit",
     "GL_NV_geometry_program4",
+    "GL_NV_gpu_shader5",
     "GL_NV_half_float",
     "GL_NV_instanced_arrays",
     "GL_NV_primitive_restart",
     "GL_NV_texture_barrier",
     "GL_NV_transform_feedback",
     "GL_NV_transform_feedback2",
     "GL_OES_EGL_image",
     "GL_OES_EGL_image_external",

--- a/gfx/gl/GLContext.h
+++ b/gfx/gl/GLContext.h
@@ -98,16 +98,17 @@ enum class GLFeature {
     framebuffer_multisample,
     framebuffer_object,
     framebuffer_object_EXT_OES,
     get_integer_indexed,
     get_integer64_indexed,
     get_query_object_i64v,
     get_query_object_iv,
     gpu_shader4,
+    gpu_shader5,
     instanced_arrays,
     instanced_non_arrays,
     internalformat_query,
     invalidate_framebuffer,
     map_buffer_range,
     occlusion_query,
     occlusion_query_boolean,
     occlusion_query2,
@@ -390,16 +391,17 @@ public:
         ARB_compatibility,
         ARB_copy_buffer,
         ARB_depth_texture,
         ARB_draw_buffers,
         ARB_draw_instanced,
         ARB_framebuffer_object,
         ARB_framebuffer_sRGB,
         ARB_geometry_shader4,
+        ARB_gpu_shader5,
         ARB_half_float_pixel,
         ARB_instanced_arrays,
         ARB_internalformat_query,
         ARB_invalidate_subdata,
         ARB_map_buffer_range,
         ARB_occlusion_query2,
         ARB_pixel_buffer_object,
         ARB_robust_buffer_access_behavior,
@@ -430,16 +432,17 @@ public:
         EXT_draw_instanced,
         EXT_draw_range_elements,
         EXT_frag_depth,
         EXT_framebuffer_blit,
         EXT_framebuffer_multisample,
         EXT_framebuffer_object,
         EXT_framebuffer_sRGB,
         EXT_gpu_shader4,
+        EXT_gpu_shader5,
         EXT_multisampled_render_to_texture,
         EXT_occlusion_query_boolean,
         EXT_packed_depth_stencil,
         EXT_read_format_bgra,
         EXT_robustness,
         EXT_sRGB,
         EXT_sRGB_write_control,
         EXT_shader_texture_lod,
@@ -461,16 +464,17 @@ public:
         KHR_robust_buffer_access_behavior,
         KHR_robustness,
         KHR_texture_compression_astc_hdr,
         KHR_texture_compression_astc_ldr,
         NV_draw_instanced,
         NV_fence,
         NV_framebuffer_blit,
         NV_geometry_program4,
+        NV_gpu_shader5,
         NV_half_float,
         NV_instanced_arrays,
         NV_primitive_restart,
         NV_texture_barrier,
         NV_transform_feedback,
         NV_transform_feedback2,
         OES_EGL_image,
         OES_EGL_image_external,

--- a/gfx/gl/GLContextFeatures.cpp
+++ b/gfx/gl/GLContextFeatures.cpp
@@ -317,16 +317,28 @@ static const FeatureInfo sFeatureInfoArr
         GLESVersion::ES3,
         GLContext::Extension_None,
         {
             GLContext::EXT_gpu_shader4,
             GLContext::Extensions_End
         }
     },
     {
+        "gpu_shader5",
+        GLVersion::GL4,
+        GLESVersion::NONE,
+        GLContext::Extension_None,
+        {
+            GLContext::ARB_gpu_shader5,
+            GLContext::EXT_gpu_shader5,
+            GLContext::NV_gpu_shader5,
+            GLContext::Extensions_End
+        }
+    },
+    {
         "instanced_arrays",
         GLVersion::GL3_3,
         GLESVersion::ES3,
         GLContext::Extension_None,
         {
             GLContext::ARB_instanced_arrays,
             GLContext::NV_instanced_arrays,
             GLContext::ANGLE_instanced_arrays,