diff --git a/dom/canvas/WebGLContext.h b/dom/canvas/WebGLContext.h
index b191a2f133a1..77b9270941b1 100644
--- a/dom/canvas/WebGLContext.h
+++ b/dom/canvas/WebGLContext.h
@@ -315,11 +315,6 @@ class WebGLContext : public VRefCounted, public SupportsWeakPtr {
 
   std::unique_ptr<gl::Texture> mIncompleteTexOverride;
 
-  // Reuse, to avoid reallocing data for this, as this is showing up in
-  // profiles.
-  std::unordered_map<uint32_t, const webgl::SamplerUniformInfo*>
-      mReuseable_ScopedResolveTexturesForDraw_samplerByTexUnit;
-
  public:
   class FuncScope;
 
diff --git a/dom/canvas/WebGLContextDraw.cpp b/dom/canvas/WebGLContextDraw.cpp
index e2bed5cbe59d..3113da76d1be 100644
--- a/dom/canvas/WebGLContextDraw.cpp
+++ b/dom/canvas/WebGLContextDraw.cpp
@@ -79,11 +79,11 @@ ScopedResolveTexturesForDraw::ScopedResolveTexturesForDraw(
     : mWebGL(webgl) {
   const auto& fb = mWebGL->mBoundDrawFramebuffer;
 
-  auto& samplerByTexUnit =
-      mWebGL->mReuseable_ScopedResolveTexturesForDraw_samplerByTexUnit;
-  if (!samplerByTexUnit.empty()) {
-    samplerByTexUnit.clear();
-  }
+  struct SamplerByTexUnit {
+    uint8_t texUnit;
+    const webgl::SamplerUniformInfo* sampler;
+  };
+  AutoTArray<SamplerByTexUnit, 8> samplerByTexUnit;
 
   MOZ_ASSERT(mWebGL->mActiveProgramLinkInfo);
   const auto& samplerUniforms = mWebGL->mActiveProgramLinkInfo->samplerUniforms;
@@ -96,11 +96,19 @@ ScopedResolveTexturesForDraw::ScopedResolveTexturesForDraw(
       MOZ_ASSERT(texUnit < texList.Length());
 
       {
-        auto& prevSamplerForTexUnit = samplerByTexUnit[texUnit];
+        decltype(SamplerByTexUnit::sampler) prevSamplerForTexUnit = nullptr;
+        for (const auto& cur : samplerByTexUnit) {
+          if (cur.texUnit == texUnit) {
+            prevSamplerForTexUnit = cur.sampler;
+          }
+        }
         if (!prevSamplerForTexUnit) {
+          samplerByTexUnit.AppendElement(SamplerByTexUnit{texUnit, &uniform});
           prevSamplerForTexUnit = &uniform;
         }
-        if (&uniform.texListForType != &prevSamplerForTexUnit->texListForType) {
+
+        if (MOZ_UNLIKELY(&uniform.texListForType !=
+                         &prevSamplerForTexUnit->texListForType)) {
           // Pointing to different tex lists means different types!
           const auto linkInfo = mWebGL->mActiveProgramLinkInfo;
           const auto LocInfoBySampler = [&](const webgl::SamplerUniformInfo* p)
@@ -132,11 +140,11 @@ ScopedResolveTexturesForDraw::ScopedResolveTexturesForDraw(
 
       const auto& sampler = mWebGL->mBoundSamplers[texUnit];
       const auto& samplingInfo = tex->GetSampleableInfo(sampler.get());
-      if (!samplingInfo) {  // There was an error.
+      if (MOZ_UNLIKELY(!samplingInfo)) {  // There was an error.
         *out_error = true;
         return;
       }
-      if (!samplingInfo->IsComplete()) {
+      if (MOZ_UNLIKELY(!samplingInfo->IsComplete())) {
         if (samplingInfo->incompleteReason) {
           const auto& targetName = GetEnumName(tex->Target().get());
           mWebGL->GenerateWarning("%s at unit %u is incomplete: %s", targetName,
@@ -148,7 +156,7 @@ ScopedResolveTexturesForDraw::ScopedResolveTexturesForDraw(
 
       // We have more validation to do if we're otherwise complete:
       const auto& texBaseType = samplingInfo->usage->format->baseType;
-      if (texBaseType != uniformBaseType) {
+      if (MOZ_UNLIKELY(texBaseType != uniformBaseType)) {
         const auto& targetName = GetEnumName(tex->Target().get());
         const auto& srcType = ToString(texBaseType);
         const auto& dstType = ToString(uniformBaseType);
@@ -160,7 +168,8 @@ ScopedResolveTexturesForDraw::ScopedResolveTexturesForDraw(
         return;
       }
 
-      if (uniform.isShadowSampler != samplingInfo->isDepthTexCompare) {
+      if (MOZ_UNLIKELY(uniform.isShadowSampler !=
+                       samplingInfo->isDepthTexCompare)) {
         const auto& targetName = GetEnumName(tex->Target().get());
         mWebGL->ErrorInvalidOperation(
             "%s at unit %u is%s a depth texture"
@@ -173,8 +182,8 @@ ScopedResolveTexturesForDraw::ScopedResolveTexturesForDraw(
         return;
       }
 
-      if (!ValidateNoSamplingFeedback(*tex, samplingInfo->levels, fb.get(),
-                                      texUnit)) {
+      if (MOZ_UNLIKELY(!ValidateNoSamplingFeedback(*tex, samplingInfo->levels,
+                                                   fb.get(), texUnit))) {
         *out_error = true;
         return;
       }
diff --git a/dom/canvas/WebGLContextGL.cpp b/dom/canvas/WebGLContextGL.cpp
index 10b1f576ad68..28cc1368649a 100644
--- a/dom/canvas/WebGLContextGL.cpp
+++ b/dom/canvas/WebGLContextGL.cpp
@@ -1355,8 +1355,8 @@ void WebGLContext::UniformData(
     const auto srcBegin = reinterpret_cast<const uint32_t*>(data.begin().get());
     auto destIndex = locInfo->indexIntoUniform;
     for (const auto& val : Range<const uint32_t>(srcBegin, elemCount)) {
-      if (destIndex >= texUnits.size()) break;
-      texUnits[destIndex] = val;
+      if (destIndex >= texUnits.Length()) break;
+      texUnits[destIndex] = AssertedCast<uint8_t>(val);
       destIndex += 1;
     }
   }
diff --git a/dom/canvas/WebGLContextValidate.cpp b/dom/canvas/WebGLContextValidate.cpp
index 1a2e673d0b22..f01ed06a3616 100644
--- a/dom/canvas/WebGLContextValidate.cpp
+++ b/dom/canvas/WebGLContextValidate.cpp
@@ -202,6 +202,8 @@ static webgl::Limits MakeLimits(const WebGLContext& webgl) {
   // GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS value is the accurate value.
   gl.GetUIntegerv(LOCAL_GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,
                   &limits.maxTexUnits);
+  limits.maxTexUnits = std::min(
+      limits.maxTexUnits, uint32_t{UINT8_MAX});  // We want to use uint8_t.
 
   gl.GetUIntegerv(LOCAL_GL_MAX_TEXTURE_SIZE, &limits.maxTex2dSize);
   gl.GetUIntegerv(LOCAL_GL_MAX_CUBE_MAP_TEXTURE_SIZE, &limits.maxTexCubeSize);
diff --git a/dom/canvas/WebGLProgram.cpp b/dom/canvas/WebGLProgram.cpp
index 586019603d8a..3dfa3a7de8b1 100644
--- a/dom/canvas/WebGLProgram.cpp
+++ b/dom/canvas/WebGLProgram.cpp
@@ -490,7 +490,7 @@ RefPtr<const webgl::LinkedProgramInfo> QueryProgramInfo(WebGLProgram* prog,
 
       auto curInfo = std::unique_ptr<webgl::SamplerUniformInfo>(
           new webgl::SamplerUniformInfo{*texList, *baseType, isShadowSampler});
-      curInfo->texUnits.resize(uniform.elemCount);
+      curInfo->texUnits.SetLength(uniform.elemCount);
       samplerInfo = curInfo.get();
       info->samplerUniforms.push_back(std::move(curInfo));
     }
diff --git a/dom/canvas/WebGLProgram.h b/dom/canvas/WebGLProgram.h
index fc7d97987abc..5d6349764db1 100644
--- a/dom/canvas/WebGLProgram.h
+++ b/dom/canvas/WebGLProgram.h
@@ -78,7 +78,7 @@ struct SamplerUniformInfo final {
   const decltype(WebGLContext::mBound2DTextures)& texListForType;
   const webgl::TextureBaseType texBaseType;
   const bool isShadowSampler;
-  std::vector<uint32_t> texUnits;
+  AutoTArray<uint8_t, 8> texUnits;
 };
 
 struct LocationInfo final {