diff --git a/dom/canvas/WebGLBuffer.cpp b/dom/canvas/WebGLBuffer.cpp
index f202c9950d1c..84589207923e 100644
--- a/dom/canvas/WebGLBuffer.cpp
+++ b/dom/canvas/WebGLBuffer.cpp
@@ -8,7 +8,6 @@
 #include "GLContext.h"
 #include "mozilla/dom/WebGLRenderingContextBinding.h"
 #include "WebGLContext.h"
-#include "WebGLElementArrayCache.h"
 
 namespace mozilla {
 
@@ -38,9 +37,6 @@ WebGLBuffer::SetContentAfterBind(GLenum target)
     switch (target) {
     case LOCAL_GL_ELEMENT_ARRAY_BUFFER:
         mContent = Kind::ElementArray;
-        if (!mCache) {
-            mCache.reset(new WebGLElementArrayCache);
-        }
         break;
 
     case LOCAL_GL_ARRAY_BUFFER:
@@ -64,7 +60,8 @@ WebGLBuffer::Delete()
     mContext->MakeContextCurrent();
     mContext->gl->fDeleteBuffers(1, &mGLName);
     mByteLength = 0;
-    mCache = nullptr;
+    mIndexCache = nullptr;
+    mIndexRanges.clear();
     LinkedListElement<WebGLBuffer>::remove(); // remove from mContext->mBuffers
 }
 
@@ -110,14 +107,9 @@ WebGLBuffer::BufferData(GLenum target, size_t size, const void* data, GLenum usa
     if (!ValidateBufferUsageEnum(mContext, funcName, usage))
         return;
 
-    const auto& gl = mContext->gl;
-    gl->MakeCurrent();
-    const ScopedLazyBind lazyBind(gl, target, this);
-    mContext->InvalidateBufferFetching();
-
 #ifdef XP_MACOSX
     // bug 790879
-    if (gl->WorkAroundDriverBugs() &&
+    if (mContext->gl->WorkAroundDriverBugs() &&
         size > INT32_MAX)
     {
         mContext->ErrorOutOfMemory("%s: Allocation size too large.", funcName);
@@ -125,10 +117,31 @@ WebGLBuffer::BufferData(GLenum target, size_t size, const void* data, GLenum usa
     }
 #endif
 
+    const void* uploadData = data;
+
+    UniqueBuffer newIndexCache;
+    if (target == LOCAL_GL_ELEMENT_ARRAY_BUFFER &&
+        mContext->mNeedsIndexValidation)
+    {
+        newIndexCache = malloc(size);
+        if (!newIndexCache) {
+            mContext->ErrorOutOfMemory("%s: Failed to alloc index cache.", funcName);
+            return;
+        }
+        memcpy(newIndexCache.get(), data, size);
+        uploadData = newIndexCache.get();
+    }
+
+    const auto& gl = mContext->gl;
+    gl->MakeCurrent();
+    const ScopedLazyBind lazyBind(gl, target, this);
+
     const bool sizeChanges = (size != ByteLength());
     if (sizeChanges) {
+        mContext->InvalidateBufferFetching();
+
         gl::GLContext::LocalErrorScope errorScope(*gl);
-        gl->fBufferData(target, size, data, usage);
+        gl->fBufferData(target, size, uploadData, usage);
         const auto error = errorScope.GetError();
 
         if (error) {
@@ -137,19 +150,54 @@ WebGLBuffer::BufferData(GLenum target, size_t size, const void* data, GLenum usa
             return;
         }
     } else {
-        gl->fBufferData(target, size, data, usage);
+        gl->fBufferData(target, size, uploadData, usage);
     }
 
     mUsage = usage;
     mByteLength = size;
+    mIndexCache = Move(newIndexCache);
 
-    // Warning: Possibly shared memory.  See bug 1225033.
-    if (!ElementArrayCacheBufferData(data, size)) {
-        mByteLength = 0;
-        mContext->ErrorOutOfMemory("%s: Failed update index buffer cache.", funcName);
+    if (mIndexCache) {
+        if (mIndexRanges.size()) {
+            mContext->GeneratePerfWarning("[%p] Invalidating %u ranges.", this,
+                                          uint32_t(mIndexRanges.size()));
+            mIndexRanges.clear();
+        }
     }
 }
 
+void
+WebGLBuffer::BufferSubData(GLenum target, size_t dstByteOffset, size_t dataLen,
+                           const void* data) const
+{
+    const char funcName[] = "bufferSubData";
+
+    if (!ValidateRange(funcName, dstByteOffset, dataLen))
+        return;
+
+    if (!CheckedInt<GLintptr>(dataLen).isValid())
+        return mContext->ErrorOutOfMemory("%s: Size too large.", funcName);
+
+    ////
+
+    const void* uploadData = data;
+    if (mIndexCache) {
+        const auto cachedDataBegin = (uint8_t*)mIndexCache.get() + dstByteOffset;
+        memcpy(cachedDataBegin, data, dataLen);
+        uploadData = cachedDataBegin;
+
+        InvalidateCacheRange(dstByteOffset, dataLen);
+    }
+
+    ////
+
+    const auto& gl = mContext->gl;
+    gl->MakeCurrent();
+    const ScopedLazyBind lazyBind(gl, target, this);
+
+    gl->fBufferSubData(target, dstByteOffset, dataLen, uploadData);
+}
+
 bool
 WebGLBuffer::ValidateRange(const char* funcName, size_t byteOffset, size_t byteLen) const
 {
@@ -171,54 +219,131 @@ WebGLBuffer::ValidateRange(const char* funcName, size_t byteOffset, size_t byteL
 
 ////////////////////////////////////////
 
-bool
-WebGLBuffer::ElementArrayCacheBufferData(const void* ptr,
-                                         size_t bufferSizeInBytes)
+static uint8_t
+IndexByteSizeByType(GLenum type)
 {
-    if (mContext->IsWebGL2())
-        return true;
-
-    if (mContent == Kind::ElementArray)
-        return mCache->BufferData(ptr, bufferSizeInBytes);
-
-    return true;
+    switch (type) {
+    case LOCAL_GL_UNSIGNED_BYTE:  return 1;
+    case LOCAL_GL_UNSIGNED_SHORT: return 2;
+    case LOCAL_GL_UNSIGNED_INT:   return 4;
+    default:
+        MOZ_CRASH();
+    }
 }
 
 void
-WebGLBuffer::ElementArrayCacheBufferSubData(size_t pos, const void* ptr,
-                                            size_t updateSizeInBytes)
+WebGLBuffer::InvalidateCacheRange(size_t byteOffset, size_t byteLength) const
 {
-    if (mContext->IsWebGL2())
-        return;
+    MOZ_ASSERT(mIndexCache);
 
-    if (mContent == Kind::ElementArray)
-        mCache->BufferSubData(pos, ptr, updateSizeInBytes);
+    std::vector<IndexRange> invalids;
+    const size_t updateBegin = byteOffset;
+    const size_t updateEnd = updateBegin + byteLength;
+    for (const auto& cur : mIndexRanges) {
+        const auto& range = cur.first;
+        const auto& indexByteSize = IndexByteSizeByType(range.type);
+        const size_t rangeBegin = range.first * indexByteSize;
+        const size_t rangeEnd = rangeBegin + range.count*indexByteSize;
+        if (rangeBegin >= updateEnd || rangeEnd <= updateBegin)
+            continue;
+        invalids.push_back(range);
+    }
+
+    if (invalids.size()) {
+        mContext->GeneratePerfWarning("[%p] Invalidating %u/%u ranges.", this,
+                                      uint32_t(invalids.size()),
+                                      uint32_t(mIndexRanges.size()));
+
+        for (const auto& cur : invalids) {
+            mIndexRanges.erase(cur);
+        }
+    }
 }
 
 size_t
 WebGLBuffer::SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
 {
-    size_t sizeOfCache = mCache ? mCache->SizeOfIncludingThis(mallocSizeOf)
-                                : 0;
-    return mallocSizeOf(this) + sizeOfCache;
+    size_t size = mallocSizeOf(this);
+    if (mIndexCache) {
+        size += mByteLength;
+    }
+    return size;
 }
 
-bool
-WebGLBuffer::Validate(GLenum type, uint32_t maxAllowed, size_t first, size_t count) const
+template<typename T>
+static size_t
+MaxForRange(const void* data, size_t first, size_t count, const uint32_t ignoredVal)
 {
-    if (mContext->IsWebGL2())
+    const T ignoredTVal(ignoredVal);
+    T ret = 0;
+
+    auto itr = (const T*)data + first;
+    const auto end = itr + count;
+
+    for (; itr != end; ++itr) {
+        const auto& val = *itr;
+        if (val <= ret)
+            continue;
+
+        if (val == ignoredTVal)
+            continue;
+
+        ret = val;
+    }
+
+    return size_t(ret);
+}
+
+const uint32_t kMaxIndexRanges = 256;
+
+bool
+WebGLBuffer::ValidateIndexedFetch(GLenum type, uint32_t numFetchable, size_t first,
+                                  size_t count) const
+{
+    if (!mIndexCache)
         return true;
 
-    return mCache->Validate(type, maxAllowed, first, count);
-}
+    if (!count)
+        return true;
 
-bool
-WebGLBuffer::IsElementArrayUsedWithMultipleTypes() const
-{
-    if (mContext->IsWebGL2())
-        return false;
+    const IndexRange range = { type, first, count };
+    auto res = mIndexRanges.insert({ range, size_t(0) });
+    if (mIndexRanges.size() > kMaxIndexRanges) {
+        mContext->GeneratePerfWarning("[%p] Clearing mIndexRanges after exceeding %u.",
+                                      this, kMaxIndexRanges);
+        mIndexRanges.clear();
+        res = mIndexRanges.insert({ range, size_t(0) });
+    }
 
-    return mCache->BeenUsedWithMultipleTypes();
+    const auto& itr = res.first;
+    const auto& didInsert = res.second;
+
+    auto& maxFetchIndex = itr->second;
+    if (didInsert) {
+        const auto& data = mIndexCache.get();
+        const uint32_t ignoreVal = (mContext->IsWebGL2() ? UINT32_MAX : 0);
+
+        switch (type) {
+        case LOCAL_GL_UNSIGNED_BYTE:
+            maxFetchIndex = MaxForRange<uint8_t>(data, first, count, ignoreVal);
+            break;
+        case LOCAL_GL_UNSIGNED_SHORT:
+            maxFetchIndex = MaxForRange<uint16_t>(data, first, count, ignoreVal);
+            break;
+        case LOCAL_GL_UNSIGNED_INT:
+            maxFetchIndex = MaxForRange<uint32_t>(data, first, count, ignoreVal);
+            break;
+        default:
+            MOZ_CRASH();
+        }
+
+        mContext->GeneratePerfWarning("[%p] New range #%u: (0x%04x, %u, %u): %u", this,
+                                      uint32_t(mIndexRanges.size()), type,
+                                      uint32_t(first), uint32_t(count),
+                                      uint32_t(maxFetchIndex));
+    }
+
+    return maxFetchIndex < numFetchable;
 }
 
 ////
diff --git a/dom/canvas/WebGLBuffer.h b/dom/canvas/WebGLBuffer.h
index 883712aad451..025ad78dc645 100644
--- a/dom/canvas/WebGLBuffer.h
+++ b/dom/canvas/WebGLBuffer.h
@@ -6,18 +6,16 @@
 #ifndef WEBGL_BUFFER_H_
 #define WEBGL_BUFFER_H_
 
+#include <map>
+
 #include "GLDefs.h"
 #include "mozilla/LinkedList.h"
-#include "mozilla/UniquePtr.h"
 #include "nsWrapperCache.h"
-
 #include "WebGLObjectModel.h"
 #include "WebGLTypes.h"
 
 namespace mozilla {
 
-class WebGLElementArrayCache;
-
 class WebGLBuffer final
     : public nsWrapperCache
     , public WebGLRefCountedObject<WebGLBuffer>
@@ -46,16 +44,9 @@ public:
     GLenum Usage() const { return mUsage; }
     size_t ByteLength() const { return mByteLength; }
 
-    bool ElementArrayCacheBufferData(const void* ptr, size_t bufferSizeInBytes);
-
-    void ElementArrayCacheBufferSubData(size_t pos, const void* ptr,
-                                        size_t updateSizeInBytes);
-
-    bool Validate(GLenum type, uint32_t max_allowed, size_t first, size_t count) const;
+    bool ValidateIndexedFetch(GLenum type, uint32_t max_allowed, size_t first, size_t count) const;
     bool ValidateRange(const char* funcName, size_t byteOffset, size_t byteLen) const;
 
-    bool IsElementArrayUsedWithMultipleTypes() const;
-
     WebGLContext* GetParentObject() const {
         return mContext;
     }
@@ -64,6 +55,8 @@ public:
 
     bool ValidateCanBindToTarget(const char* funcName, GLenum target);
     void BufferData(GLenum target, size_t size, const void* data, GLenum usage);
+    void BufferSubData(GLenum target, size_t dstByteOffset, size_t dataLen,
+                       const void* data) const;
 
     ////
 
@@ -102,12 +95,32 @@ public:
 protected:
     ~WebGLBuffer();
 
+    void InvalidateCacheRange(size_t offset, size_t length) const;
+
     Kind mContent;
     GLenum mUsage;
     size_t mByteLength;
-    UniquePtr<WebGLElementArrayCache> mCache;
     size_t mTFBindCount;
     size_t mNonTFBindCount;
+
+    struct IndexRange final {
+        GLenum type;
+        size_t first;
+        size_t count;
+
+        bool operator<(const IndexRange& x) const {
+            if (type != x.type)
+                return type < x.type;
+
+            if (first != x.first)
+                return first < x.first;
+
+            return count < x.count;
+        }
+    };
+
+    UniqueBuffer mIndexCache;
+    mutable std::map<IndexRange, size_t> mIndexRanges;
 };
 
 } // namespace mozilla
diff --git a/dom/canvas/WebGLContext.h b/dom/canvas/WebGLContext.h
index 8147a32ff821..ce0e5e544618 100644
--- a/dom/canvas/WebGLContext.h
+++ b/dom/canvas/WebGLContext.h
@@ -2114,50 +2114,6 @@ ValidateTexImageTarget(WebGLContext* webgl, const char* funcName, uint8_t funcDi
                        GLenum rawTexImageTarget, TexImageTarget* const out_texImageTarget,
                        WebGLTexture** const out_tex);
 
-class UniqueBuffer
-{
-    // Like UniquePtr<>, but for void* and malloc/calloc/free.
-    void* mBuffer;
-
-public:
-    UniqueBuffer()
-        : mBuffer(nullptr)
-    { }
-
-    MOZ_IMPLICIT UniqueBuffer(void* buffer)
-        : mBuffer(buffer)
-    { }
-
-    ~UniqueBuffer() {
-        free(mBuffer);
-    }
-
-    UniqueBuffer(UniqueBuffer&& other) {
-        this->mBuffer = other.mBuffer;
-        other.mBuffer = nullptr;
-    }
-
-    UniqueBuffer& operator =(UniqueBuffer&& other) {
-        free(this->mBuffer);
-        this->mBuffer = other.mBuffer;
-        other.mBuffer = nullptr;
-        return *this;
-    }
-
-    UniqueBuffer& operator =(void* newBuffer) {
-        free(this->mBuffer);
-        this->mBuffer = newBuffer;
-        return *this;
-    }
-
-    explicit operator bool() const { return bool(mBuffer); }
-
-    void* get() const { return mBuffer; }
-
-    UniqueBuffer(const UniqueBuffer& other) = delete; // construct using Move()!
-    void operator =(const UniqueBuffer& other) = delete; // assign using Move()!
-};
-
 class ScopedUnpackReset final
     : public gl::ScopedGLWrapper<ScopedUnpackReset>
 {
diff --git a/dom/canvas/WebGLContextBuffers.cpp b/dom/canvas/WebGLContextBuffers.cpp
index 68cceb009742..776b6c883de2 100644
--- a/dom/canvas/WebGLContextBuffers.cpp
+++ b/dom/canvas/WebGLContextBuffers.cpp
@@ -402,27 +402,11 @@ WebGLContext::BufferSubDataImpl(GLenum target, WebGLsizeiptr dstByteOffset,
     if (!buffer)
         return;
 
-    if (!buffer->ValidateRange(funcName, dstByteOffset, dataLen))
-        return;
-
-    if (!CheckedInt<GLintptr>(dataLen).isValid()) {
-        ErrorOutOfMemory("%s: Size too large.", funcName);
-        return;
-    }
-    const GLintptr glDataLen(dataLen);
-
-    ////
-
-    MakeContextCurrent();
-    const ScopedLazyBind lazyBind(gl, target, buffer);
-
-    // Warning: Possibly shared memory.  See bug 1225033.
-    gl->fBufferSubData(target, dstByteOffset, glDataLen, data);
-
-    // Warning: Possibly shared memory.  See bug 1225033.
-    buffer->ElementArrayCacheBufferSubData(dstByteOffset, data, size_t(glDataLen));
+    buffer->BufferSubData(target, size_t(dstByteOffset), dataLen, data);
 }
 
+////
+
 void
 WebGLContext::BufferSubData(GLenum target, WebGLsizeiptr dstByteOffset,
                             const dom::ArrayBuffer& src)
diff --git a/dom/canvas/WebGLContextDraw.cpp b/dom/canvas/WebGLContextDraw.cpp
index 867e47cbdc69..92ca2ea89aa6 100644
--- a/dom/canvas/WebGLContextDraw.cpp
+++ b/dom/canvas/WebGLContextDraw.cpp
@@ -738,7 +738,7 @@ WebGLContext::DrawElements_check(const char* funcName, GLenum mode, GLsizei vert
         return false;
 
     if (!mMaxFetchedVertices ||
-        !elemArrayBuffer.Validate(type, mMaxFetchedVertices - 1, first, vertCount))
+        !elemArrayBuffer.ValidateIndexedFetch(type, mMaxFetchedVertices, first, vertCount))
     {
         ErrorInvalidOperation("%s: bound vertex attribute buffers do not have sufficient "
                               "size for given indices from the bound element array",
@@ -746,15 +746,6 @@ WebGLContext::DrawElements_check(const char* funcName, GLenum mode, GLsizei vert
         return false;
     }
 
-    // Bug 1008310 - Check if buffer has been used with a different previous type
-    if (elemArrayBuffer.IsElementArrayUsedWithMultipleTypes()) {
-        nsCString typeName;
-        WebGLContext::EnumName(type, &typeName);
-        GenerateWarning("%s: bound element array buffer previously used with a type other than "
-                        "%s, this will affect performance.",
-                        funcName, typeName.BeginReading());
-    }
-
     return true;
 }
 
@@ -994,8 +985,8 @@ WebGLContext::ValidateBufferFetching(const char* info)
             maxInstances = 0;
             break;
         }
-        availBytes -= vd.BytesPerVertex();
-        const size_t vertCapacity = 1 + availBytes / vd.ExplicitStride();
+        availBytes -= vd.BytesPerVertex(); // Snip off the tail.
+        const size_t vertCapacity = availBytes / vd.ExplicitStride() + 1; // Add +1 for the snipped tail.
 
         if (vd.mDivisor == 0) {
             if (vertCapacity < maxVertices) {
diff --git a/dom/canvas/WebGLElementArrayCache.cpp b/dom/canvas/WebGLElementArrayCache.cpp
deleted file mode 100644
index a0591445a06e..000000000000
--- a/dom/canvas/WebGLElementArrayCache.cpp
+++ /dev/null
@@ -1,622 +0,0 @@
-/* -*- 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 "WebGLElementArrayCache.h"
-
-#include <algorithm>
-#include <cstdlib>
-#include <cstring>
-#include <limits>
-#include "mozilla/Assertions.h"
-#include "mozilla/MathAlgorithms.h"
-#include "mozilla/MemoryReporting.h"
-
-namespace mozilla {
-
-/* WebGLElementArrayCacheTree contains most of the implementation of
- * WebGLElementArrayCache, which performs WebGL element array buffer validation
- * for drawElements.
- *
- * Attention: Here lie nontrivial data structures, bug-prone algorithms, and
- * non-canonical tweaks! Whence the explanatory comments, and compiled unit
- * test.
- *
- * *** What problem are we solving here? ***
- *
- * WebGL::DrawElements has to validate that the elements are in range wrt the
- * current vertex attribs. This boils down to the problem, given an array of
- * integers, of computing the maximum in an arbitrary sub-array. The naive
- * algorithm has linear complexity; this has been a major performance problem,
- * see bug 569431. In that bug, we took the approach of caching the max for the
- * whole array, which does cover most cases (DrawElements typically consumes the
- * whole element array buffer) but doesn't help in other use cases:
- *  - when doing "partial DrawElements" i.e. consuming only part of the element
- *    array buffer
- *  - when doing frequent "partial buffer updates" i.e. bufferSubData calls
- *    updating parts of the element array buffer
- *
- * *** The solution: A binary tree ***
- *
- * The solution implemented here is to use a binary tree as the cache data
- * structure. Each tree node contains the max of its two children nodes. In this
- * way, finding the maximum in any contiguous sub-array has log complexity
- * instead of linear complexity.
- *
- * Simplistically, if the element array is:
- *
- *    [1   4   3   2]
- *
- * then the corresponding tree is:
- *
- *           4
- *         _/ \_
- *       4       3
- *      / \     / \
- *     1   4   3   2
- *
- * In practice, the bottom-most levels of the tree are both the largest to store
- * (because they have more nodes), and the least useful performance-wise
- * (because each node in the bottom levels concerns only few entries in the
- * elements array buffer, it is cheap to compute).
- *
- * For this reason, we stop the tree a few levels above, so that each tree leaf
- * actually corresponds to more than one element array entry.
- *
- * The number of levels that we "drop" is |kSkippedBottomTreeLevels| and the
- * number of element array entries that each leaf corresponds to, is
- * |kElementsPerLeaf|. This being a binary tree, we have:
- *
- *   kElementsPerLeaf = 2 ^ kSkippedBottomTreeLevels.
- *
- * *** Storage layout of the binary tree ***
- *
- * We take advantage of the specifics of the situation to avoid generalist tree
- * storage and instead store the tree entries in a vector, mTreeData.
- *
- * TreeData is always a vector of length:
- *
- *    2 * (number of leaves).
- *
- * Its data layout is as follows: mTreeData[0] is unused, mTreeData[1] is the
- * root node, then at offsets 2..3 is the tree level immediately below the root
- * node, then at offsets 4..7 is the tree level below that, etc.
- *
- * The figure below illustrates this by writing at each tree node the offset
- * into mTreeData at which it is stored:
- *
- *           1
- *         _/ \_
- *       2       3
- *      / \     / \
- *     4   5   6   7
- *    ...
- *
- * Thus, under the convention that the root level is level 0, we see that level
- * N is stored at offsets:
- *
- *    [ 2^n .. 2^(n+1) - 1 ]
- *
- * in mTreeData. Likewise, all the usual tree operations have simple
- * mathematical expressions in terms of mTreeData offsets, see all the methods
- * such as ParentNode, LeftChildNode, etc.
- *
- * *** Design constraint: Element types aren't known at buffer-update time ***
- *
- * Note that a key constraint that we're operating under, is that we don't know
- * the types of the elements by the time WebGL bufferData/bufferSubData methods
- * are called. The type of elements is only specified in the drawElements call.
- * This means that we may potentially have to store caches for multiple element
- * types, for the same element array buffer. Since we don't know yet how many
- * element types we'll eventually support (extensions add more), the concern
- * about memory usage is serious. This is addressed by kSkippedBottomTreeLevels
- * as explained above. Of course, in the typical case where each element array
- * buffer is only ever used with one type, this is also addressed by having
- * WebGLElementArrayCache lazily create trees for each type only upon first use.
- *
- * Another consequence of this constraint is that when updating the trees, we
- * have to update all existing trees. So if trees for types uint8_t, uint16_t
- * and uint32_t have ever been constructed for this buffer, every subsequent
- * update will have to update all trees even if one of the types is never used
- * again. That's inefficient, but content should not put indices of different
- * types in the same element array buffer anyways. Different index types can
- * only be consumed in separate drawElements calls, so nothing particular is
- * to be achieved by lumping them in the same buffer object.
- */
-template<typename T>
-struct WebGLElementArrayCacheTree
-{
-    /* A too-high kSkippedBottomTreeLevels would harm the performance of small
-     * drawElements calls. A too-low kSkippedBottomTreeLevels would cause undue
-     * memory usage. The current value has been validated by some benchmarking.
-     * See bug 732660.
-     */
-    static const size_t kSkippedBottomTreeLevels = 3;
-    static const size_t kElementsPerLeaf = 1 << kSkippedBottomTreeLevels;
-    // Since kElementsPerLeaf is POT:
-    static const size_t kElementsPerLeafMask = kElementsPerLeaf - 1;
-
-private:
-    // The WebGLElementArrayCache that owns this tree:
-    WebGLElementArrayCache& mParent;
-
-    // The tree's internal data storage. Its length is 2 * (number of leaves)
-    // because of its data layout explained in the above class comment.
-    FallibleTArray<T> mTreeData;
-
-public:
-    // Constructor. Takes a reference to the WebGLElementArrayCache that is to be
-    // the parent. Does not initialize the tree. Should be followed by a call
-    // to Update() to attempt initializing the tree.
-    explicit WebGLElementArrayCacheTree(WebGLElementArrayCache& value)
-        : mParent(value)
-    {
-    }
-
-    T GlobalMaximum() const {
-        return mTreeData[1];
-    }
-
-    // returns the index of the parent node; if treeIndex=1 (the root node),
-    // the return value is 0.
-    static size_t ParentNode(size_t treeIndex) {
-        MOZ_ASSERT(treeIndex > 1);
-        return treeIndex >> 1;
-    }
-
-    static bool IsRightNode(size_t treeIndex) {
-        MOZ_ASSERT(treeIndex > 1);
-        return treeIndex & 1;
-    }
-
-    static bool IsLeftNode(size_t treeIndex) {
-        MOZ_ASSERT(treeIndex > 1);
-        return !IsRightNode(treeIndex);
-    }
-
-    static size_t SiblingNode(size_t treeIndex) {
-        MOZ_ASSERT(treeIndex > 1);
-        return treeIndex ^ 1;
-    }
-
-    static size_t LeftChildNode(size_t treeIndex) {
-        MOZ_ASSERT(treeIndex);
-        return treeIndex << 1;
-    }
-
-    static size_t RightChildNode(size_t treeIndex) {
-        MOZ_ASSERT(treeIndex);
-        return SiblingNode(LeftChildNode(treeIndex));
-    }
-
-    static size_t LeftNeighborNode(size_t treeIndex, size_t distance = 1) {
-        MOZ_ASSERT(treeIndex > 1);
-        return treeIndex - distance;
-    }
-
-    static size_t RightNeighborNode(size_t treeIndex, size_t distance = 1) {
-        MOZ_ASSERT(treeIndex > 1);
-        return treeIndex + distance;
-    }
-
-    size_t NumLeaves() const {
-        // See class comment for why we the tree storage size is 2 * numLeaves.
-        return mTreeData.Length() >> 1;
-    }
-
-    size_t LeafForElement(size_t element) const {
-        size_t leaf = element / kElementsPerLeaf;
-        MOZ_ASSERT(leaf < NumLeaves());
-        return leaf;
-    }
-
-    size_t LeafForByte(size_t byte) const {
-        return LeafForElement(byte / sizeof(T));
-    }
-
-    // Returns the index, into the tree storage, where a given leaf is stored.
-    size_t TreeIndexForLeaf(size_t leaf) const {
-        // See above class comment. The tree storage is an array of length
-        // 2 * numLeaves. The leaves are stored in its second half.
-        return leaf + NumLeaves();
-    }
-
-    static size_t LastElementUnderSameLeaf(size_t element) {
-        return element | kElementsPerLeafMask;
-    }
-
-    static size_t FirstElementUnderSameLeaf(size_t element) {
-        return element & ~kElementsPerLeafMask;
-    }
-
-    static size_t NextMultipleOfElementsPerLeaf(size_t numElements) {
-        MOZ_ASSERT(numElements >= 1);
-        return ((numElements - 1) | kElementsPerLeafMask) + 1;
-    }
-
-    bool Validate(T maxAllowed, size_t firstLeaf, size_t lastLeaf)
-    {
-        size_t firstTreeIndex = TreeIndexForLeaf(firstLeaf);
-        size_t lastTreeIndex  = TreeIndexForLeaf(lastLeaf);
-
-        while (true) {
-            // Given that we tweak these values in nontrivial ways, it doesn't
-            // hurt to do this sanity check.
-            MOZ_ASSERT(firstTreeIndex <= lastTreeIndex);
-
-            // Final case where there is only one node to validate at the
-            // current tree level:
-            if (lastTreeIndex == firstTreeIndex) {
-                const T& curData = mTreeData[firstTreeIndex];
-                return curData <= maxAllowed;
-            }
-
-            // If the first node at current tree level is a right node, handle
-            // it individually and replace it with its right neighbor, which is
-            // a left node.
-            if (IsRightNode(firstTreeIndex)) {
-                const T& curData = mTreeData[firstTreeIndex];
-                if (curData > maxAllowed)
-                  return false;
-
-                firstTreeIndex = RightNeighborNode(firstTreeIndex);
-            }
-
-            // If the last node at current tree level is a left node, handle it
-            // individually and replace it with its left neighbor, which is a
-            // right node.
-            if (IsLeftNode(lastTreeIndex)) {
-                const T& curData = mTreeData[lastTreeIndex];
-                if (curData > maxAllowed)
-                    return false;
-
-                lastTreeIndex = LeftNeighborNode(lastTreeIndex);
-            }
-
-            /* At this point it can happen that firstTreeIndex and lastTreeIndex
-             * "crossed" eachother. That happens if firstTreeIndex was a right
-             * node and lastTreeIndex was its right neighor: In that case, both
-             * above tweaks happened and as a result, they ended up being
-             * swapped: LastTreeIndex is now the _left_ neighbor of
-             * firstTreeIndex. When that happens, there is nothing left to
-             * validate.
-             */
-            if (lastTreeIndex == LeftNeighborNode(firstTreeIndex))
-                return true;
-
-            // Walk up one level.
-            firstTreeIndex = ParentNode(firstTreeIndex);
-            lastTreeIndex = ParentNode(lastTreeIndex);
-        }
-    }
-
-    // Updates the tree from the parent's buffer contents. Fallible, as it
-    // may have to resize the tree storage.
-    bool Update(size_t firstByte, size_t lastByte);
-
-    size_t SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
-    {
-        return mallocSizeOf(this) +
-               mTreeData.ShallowSizeOfExcludingThis(mallocSizeOf);
-    }
-};
-
-// TreeForType: just a template helper to select the right tree object for a given
-// element type.
-template<typename T>
-struct TreeForType {};
-
-template<>
-struct TreeForType<uint8_t>
-{
-    static UniquePtr<WebGLElementArrayCacheTree<uint8_t>>&
-    Value(WebGLElementArrayCache* b) {
-        return b->mUint8Tree;
-    }
-};
-
-template<>
-struct TreeForType<uint16_t>
-{
-    static UniquePtr<WebGLElementArrayCacheTree<uint16_t>>&
-    Value(WebGLElementArrayCache* b) {
-        return b->mUint16Tree;
-    }
-};
-
-template<>
-struct TreeForType<uint32_t>
-{
-    static UniquePtr<WebGLElementArrayCacheTree<uint32_t>>&
-    Value(WebGLElementArrayCache* b) {
-        return b->mUint32Tree;
-    }
-};
-
-// Calling this method will 1) update the leaves in this interval
-// from the raw buffer data, and 2) propagate this update up the tree.
-template<typename T>
-bool
-WebGLElementArrayCacheTree<T>::Update(size_t firstByte, size_t lastByte)
-{
-    MOZ_ASSERT(firstByte <= lastByte);
-    MOZ_ASSERT(lastByte < mParent.mBytes.Length());
-
-    size_t numberOfElements = mParent.mBytes.Length() / sizeof(T);
-    size_t requiredNumLeaves = 0;
-    if (numberOfElements > 0) {
-        /* If we didn't require the number of leaves to be a power of two, then
-         * it would just be equal to
-         *
-         *    ceil(numberOfElements / kElementsPerLeaf)
-         *
-         * The way we implement this (division+ceil) operation in integer
-         * arithmetic
-         * is as follows:
-         */
-        size_t numLeavesNonPOT = (numberOfElements + kElementsPerLeaf - 1) / kElementsPerLeaf;
-        // It only remains to round that up to the next power of two:
-        requiredNumLeaves = RoundUpPow2(numLeavesNonPOT);
-    }
-
-    // Step #0: If needed, resize our tree data storage.
-    if (requiredNumLeaves != NumLeaves()) {
-        // See class comment for why we the tree storage size is 2 * numLeaves.
-        if (!mTreeData.SetLength(2 * requiredNumLeaves, fallible)) {
-            mTreeData.Clear();
-            return false;
-        }
-        MOZ_ASSERT(NumLeaves() == requiredNumLeaves);
-
-        if (NumLeaves()) {
-            // When resizing, update the whole tree, not just the subset
-            // corresponding to the part of the buffer being updated.
-            memset(mTreeData.Elements(), 0, mTreeData.Length() * sizeof(T));
-            firstByte = 0;
-            lastByte = mParent.mBytes.Length() - 1;
-        }
-    }
-
-    if (NumLeaves() == 0)
-        return true;
-
-    lastByte = std::min(lastByte, NumLeaves() * kElementsPerLeaf * sizeof(T) - 1);
-    if (firstByte > lastByte)
-        return true;
-
-    size_t firstLeaf = LeafForByte(firstByte);
-    size_t lastLeaf = LeafForByte(lastByte);
-
-    MOZ_ASSERT(firstLeaf <= lastLeaf && lastLeaf < NumLeaves());
-
-    size_t firstTreeIndex = TreeIndexForLeaf(firstLeaf);
-    size_t lastTreeIndex = TreeIndexForLeaf(lastLeaf);
-
-    // Step #1: Initialize the tree leaves from plain buffer data.
-    // That is, each tree leaf must be set to the max of the |kElementsPerLeaf|
-    // corresponding buffer entries.
-
-    // Condition-less scope to prevent leaking this scope's variables into the
-    // code below:
-    {
-        // TreeIndex is the index of the tree leaf we're writing, i.e. the
-        // destination index.
-        size_t treeIndex = firstTreeIndex;
-        // srcIndex is the index in the source buffer.
-        size_t srcIndex = firstLeaf * kElementsPerLeaf;
-        while (treeIndex <= lastTreeIndex) {
-            T m = 0;
-            size_t a = srcIndex;
-            size_t srcIndexNextLeaf = std::min(a + kElementsPerLeaf, numberOfElements);
-            for (; srcIndex < srcIndexNextLeaf; srcIndex++) {
-                m = std::max(m, mParent.Element<T>(srcIndex));
-            }
-            mTreeData[treeIndex] = m;
-            treeIndex++;
-        }
-    }
-
-    // Step #2: Propagate the values up the tree. This is simply a matter of
-    // walking up the tree and setting each node to the max of its two children.
-    while (firstTreeIndex > 1) {
-        // Move up one level.
-        firstTreeIndex = ParentNode(firstTreeIndex);
-        lastTreeIndex = ParentNode(lastTreeIndex);
-
-        // Fast-exit case where only one node is updated at the current level.
-        if (firstTreeIndex == lastTreeIndex) {
-            mTreeData[firstTreeIndex] = std::max(mTreeData[LeftChildNode(firstTreeIndex)], mTreeData[RightChildNode(firstTreeIndex)]);
-            continue;
-        }
-
-        size_t child = LeftChildNode(firstTreeIndex);
-        size_t parent = firstTreeIndex;
-        while (parent <= lastTreeIndex) {
-            T a = mTreeData[child];
-            child = RightNeighborNode(child);
-            T b = mTreeData[child];
-            child = RightNeighborNode(child);
-            mTreeData[parent] = std::max(a, b);
-            parent = RightNeighborNode(parent);
-        }
-    }
-
-    return true;
-}
-
-WebGLElementArrayCache::WebGLElementArrayCache()
-{
-}
-
-WebGLElementArrayCache::~WebGLElementArrayCache()
-{
-}
-
-bool
-WebGLElementArrayCache::BufferData(const void* ptr, size_t byteLength)
-{
-    if (mBytes.Length() != byteLength) {
-        if (!mBytes.SetLength(byteLength, fallible)) {
-            mBytes.Clear();
-            return false;
-        }
-    }
-    MOZ_ASSERT(mBytes.Length() == byteLength);
-    return BufferSubData(0, ptr, byteLength);
-}
-
-bool
-WebGLElementArrayCache::BufferSubData(size_t pos, const void* ptr,
-                                      size_t updateByteLength)
-{
-    MOZ_ASSERT(pos + updateByteLength <= mBytes.Length());
-    if (!updateByteLength)
-        return true;
-
-    // Note, using memcpy on shared racy data is not well-defined, this
-    // will need to use safe-for-races operations when those become available.
-    // See bug 1225033.
-    if (ptr)
-        memcpy(mBytes.Elements() + pos, ptr, updateByteLength);
-    else
-        memset(mBytes.Elements() + pos, 0, updateByteLength);
-    return UpdateTrees(pos, pos + updateByteLength - 1);
-}
-
-bool
-WebGLElementArrayCache::UpdateTrees(size_t firstByte, size_t lastByte)
-{
-    bool result = true;
-    if (mUint8Tree)
-        result &= mUint8Tree->Update(firstByte, lastByte);
-    if (mUint16Tree)
-        result &= mUint16Tree->Update(firstByte, lastByte);
-    if (mUint32Tree)
-        result &= mUint32Tree->Update(firstByte, lastByte);
-    return result;
-}
-
-template<typename T>
-bool
-WebGLElementArrayCache::Validate(uint32_t maxAllowed, size_t firstElement,
-                                 size_t countElements)
-{
-    // If maxAllowed is >= the max T value, then there is no way that a T index
-    // could be invalid.
-    uint32_t maxTSize = std::numeric_limits<T>::max();
-    if (maxAllowed >= maxTSize)
-        return true;
-
-    T maxAllowedT(maxAllowed);
-
-    // Integer overflow must have been handled earlier, so we assert that
-    // maxAllowedT is exactly the max allowed value.
-    MOZ_ASSERT(uint32_t(maxAllowedT) == maxAllowed);
-
-    if (!mBytes.Length() || !countElements)
-      return true;
-
-    UniquePtr<WebGLElementArrayCacheTree<T>>& tree = TreeForType<T>::Value(this);
-    if (!tree) {
-        tree = MakeUnique<WebGLElementArrayCacheTree<T>>(*this);
-        if (mBytes.Length()) {
-            bool valid = tree->Update(0, mBytes.Length() - 1);
-            if (!valid) {
-                // Do not assert here. This case would happen if an allocation
-                // failed. We've already settled on fallible allocations around
-                // here.
-                tree = nullptr;
-                return false;
-            }
-        }
-    }
-
-    size_t lastElement = firstElement + countElements - 1;
-
-    // Fast-exit path when the global maximum for the whole element array buffer
-    // falls in the allowed range:
-    T globalMax = tree->GlobalMaximum();
-    if (globalMax <= maxAllowedT)
-        return true;
-
-    const T* elements = Elements<T>();
-
-    // Before calling tree->Validate, we have to validate ourselves the
-    // boundaries of the elements span, to round them to the nearest multiple of
-    // kElementsPerLeaf.
-    size_t firstElementAdjustmentEnd = std::min(lastElement,
-                                                tree->LastElementUnderSameLeaf(firstElement));
-    while (firstElement <= firstElementAdjustmentEnd) {
-        const T& curData = elements[firstElement];
-        if (curData > maxAllowedT)
-            return false;
-
-        firstElement++;
-    }
-    size_t lastElementAdjustmentEnd = std::max(firstElement,
-                                               tree->FirstElementUnderSameLeaf(lastElement));
-    while (lastElement >= lastElementAdjustmentEnd) {
-        const T& curData = elements[lastElement];
-        if (curData > maxAllowedT)
-            return false;
-
-        lastElement--;
-    }
-
-    // at this point, for many tiny validations, we're already done.
-    if (firstElement > lastElement)
-        return true;
-
-    // general case
-    return tree->Validate(maxAllowedT, tree->LeafForElement(firstElement),
-                          tree->LeafForElement(lastElement));
-}
-
-bool
-WebGLElementArrayCache::Validate(GLenum type, uint32_t maxAllowed,
-                                 size_t firstElement, size_t countElements)
-{
-    if (type == LOCAL_GL_UNSIGNED_BYTE)
-        return Validate<uint8_t>(maxAllowed, firstElement, countElements);
-    if (type == LOCAL_GL_UNSIGNED_SHORT)
-        return Validate<uint16_t>(maxAllowed, firstElement, countElements);
-    if (type == LOCAL_GL_UNSIGNED_INT)
-        return Validate<uint32_t>(maxAllowed, firstElement, countElements);
-
-    MOZ_ASSERT(false, "Invalid type.");
-    return false;
-}
-
-template<typename T>
-static size_t
-SizeOfNullable(mozilla::MallocSizeOf mallocSizeOf, const T& obj)
-{
-    if (!obj)
-        return 0;
-    return obj->SizeOfIncludingThis(mallocSizeOf);
-}
-
-size_t
-WebGLElementArrayCache::SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
-{
-    return mallocSizeOf(this) +
-           mBytes.ShallowSizeOfExcludingThis(mallocSizeOf) +
-           SizeOfNullable(mallocSizeOf, mUint8Tree) +
-           SizeOfNullable(mallocSizeOf, mUint16Tree) +
-           SizeOfNullable(mallocSizeOf, mUint32Tree);
-}
-
-bool
-WebGLElementArrayCache::BeenUsedWithMultipleTypes() const
-{
-  // C++ Standard ($4.7)
-  // "If the source type is bool, the value false is converted to zero and
-  //  the value true is converted to one."
-  const int num_types_used = (mUint8Tree  != nullptr) +
-                             (mUint16Tree != nullptr) +
-                             (mUint32Tree != nullptr);
-  return num_types_used > 1;
-}
-
-} // end namespace mozilla
diff --git a/dom/canvas/WebGLElementArrayCache.h b/dom/canvas/WebGLElementArrayCache.h
deleted file mode 100644
index eba0535a237e..000000000000
--- a/dom/canvas/WebGLElementArrayCache.h
+++ /dev/null
@@ -1,101 +0,0 @@
-/* -*- 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/. */
-
-#ifndef WEBGL_ELEMENT_ARRAY_CACHE_H
-#define WEBGL_ELEMENT_ARRAY_CACHE_H
-
-#include "GLDefs.h"
-#include "mozilla/MemoryReporting.h"
-#include "mozilla/UniquePtr.h"
-#include "nscore.h"
-#include "nsTArray.h"
-#include <stdint.h>
-
-namespace mozilla {
-
-template<typename T>
-struct WebGLElementArrayCacheTree;
-
-/* WebGLElementArrayCache implements WebGL element array buffer validation for
- * drawElements.
- *
- * Its exposes methods meant to be called by WebGL method implementations:
- *
- * - Validate, to be called by WebGLContext::DrawElements, is where we use the
- *   cache.
- *
- * - BufferData and BufferSubData, to be called by eponymous WebGL methods, are
- *   how data is fed into the cache.
- *
- * Most of the implementation is hidden in the auxilary class template,
- * WebGLElementArrayCacheTree. Refer to its code for design comments.
- */
-class WebGLElementArrayCache {
-public:
-    bool BufferData(const void* ptr, size_t byteLength);
-    bool BufferSubData(size_t pos, const void* ptr, size_t updateByteSize);
-
-    bool Validate(GLenum type, uint32_t maxAllowed, size_t first, size_t count);
-
-    template<typename T>
-    T Element(size_t i) const { return Elements<T>()[i]; }
-
-    WebGLElementArrayCache();
-    ~WebGLElementArrayCache();
-
-    size_t SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
-    bool BeenUsedWithMultipleTypes() const;
-
-private:
-    /* Returns true if a drawElements call with the given parameters should
-     * succeed, false otherwise.
-     *
-     * In other words, this returns true if all entries in the element array at
-     * positions:
-     *
-     *    first .. first+count-1
-     *
-     * are less than or equal to maxAllowed.
-     *
-     * Input parameters:
-     *   maxAllowed: Maximum value to be allowed in the specificied portion of
-     *               the element array.
-     *   first: Start of the portion of the element array to consume.
-     *   count: Number of entries from the element array to consume.
-     *
-     * Output parameter:
-     *   out_upperBound: Upon success, is set to the actual maximum value in the
-     *                   specified range, which is then guaranteed to be less
-     *                   than or equal to maxAllowed. upon failure, is set to
-     *                   the first value in the specified range, that is greater
-     *                   than maxAllowed.
-     */
-    template<typename T>
-    bool Validate(uint32_t maxAllowed, size_t first, size_t count);
-
-    template<typename T>
-    const T* Elements() const {
-        return reinterpret_cast<const T*>(mBytes.Elements());
-    }
-
-    template<typename T>
-    T* Elements() { return reinterpret_cast<T*>(mBytes.Elements()); }
-
-    bool UpdateTrees(size_t firstByte, size_t lastByte);
-
-    template<typename T>
-    friend struct WebGLElementArrayCacheTree;
-    template<typename T>
-    friend struct TreeForType;
-
-    FallibleTArray<uint8_t> mBytes;
-    UniquePtr<WebGLElementArrayCacheTree<uint8_t>> mUint8Tree;
-    UniquePtr<WebGLElementArrayCacheTree<uint16_t>> mUint16Tree;
-    UniquePtr<WebGLElementArrayCacheTree<uint32_t>> mUint32Tree;
-};
-
-} // end namespace mozilla
-
-#endif // WEBGL_ELEMENT_ARRAY_CACHE_H
diff --git a/dom/canvas/WebGLTypes.h b/dom/canvas/WebGLTypes.h
index 448e232d4826..ac6145bf6f4b 100644
--- a/dom/canvas/WebGLTypes.h
+++ b/dom/canvas/WebGLTypes.h
@@ -173,6 +173,50 @@ enum class WebGLExtensionID : uint8_t {
     Unknown
 };
 
+class UniqueBuffer
+{
+    // Like UniquePtr<>, but for void* and malloc/calloc/free.
+    void* mBuffer;
+
+public:
+    UniqueBuffer()
+        : mBuffer(nullptr)
+    { }
+
+    MOZ_IMPLICIT UniqueBuffer(void* buffer)
+        : mBuffer(buffer)
+    { }
+
+    ~UniqueBuffer() {
+        free(mBuffer);
+    }
+
+    UniqueBuffer(UniqueBuffer&& other) {
+        this->mBuffer = other.mBuffer;
+        other.mBuffer = nullptr;
+    }
+
+    UniqueBuffer& operator =(UniqueBuffer&& other) {
+        free(this->mBuffer);
+        this->mBuffer = other.mBuffer;
+        other.mBuffer = nullptr;
+        return *this;
+    }
+
+    UniqueBuffer& operator =(void* newBuffer) {
+        free(this->mBuffer);
+        this->mBuffer = newBuffer;
+        return *this;
+    }
+
+    explicit operator bool() const { return bool(mBuffer); }
+
+    void* get() const { return mBuffer; }
+
+    UniqueBuffer(const UniqueBuffer& other) = delete; // construct using Move()!
+    void operator =(const UniqueBuffer& other) = delete; // assign using Move()!
+};
+
 } // namespace mozilla
 
 #endif
diff --git a/dom/canvas/gtest/TestWebGLElementArrayCache.cpp b/dom/canvas/gtest/TestWebGLElementArrayCache.cpp
deleted file mode 100644
index c8ffc8701fdd..000000000000
--- a/dom/canvas/gtest/TestWebGLElementArrayCache.cpp
+++ /dev/null
@@ -1,206 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* 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 "mozilla/Assertions.h"
-
-#include "WebGLElementArrayCache.h"
-
-#include <cstdio>
-#include <cstdlib>
-#include "nscore.h"
-#include "nsTArray.h"
-
-void
-MakeRandomVector(nsTArray<uint8_t>& a, size_t size)
-{
-  a.SetLength(size);
-  // only the most-significant bits of rand() are reasonably random.
-  // RAND_MAX can be as low as 0x7fff, and we need 8 bits for the result, so we can only
-  // ignore the 7 least significant bits.
-  for (size_t i = 0; i < size; i++)
-    a[i] = static_cast<uint8_t>((unsigned int)(rand()) >> 7);
-}
-
-template<typename T>
-T
-RandomInteger(T a, T b)
-{
-  T result(a + rand() % (b - a + 1));
-  return result;
-}
-
-template<typename T>
-GLenum
-GLType()
-{
-  switch (sizeof(T)) {
-  case 4:  return LOCAL_GL_UNSIGNED_INT;
-  case 2:  return LOCAL_GL_UNSIGNED_SHORT;
-  case 1:  return LOCAL_GL_UNSIGNED_BYTE;
-  default:
-    MOZ_RELEASE_ASSERT(false);
-    return 0;
-  }
-}
-
-void
-CheckValidate(bool expectSuccess, mozilla::WebGLElementArrayCache& c, GLenum type,
-              uint32_t maxAllowed, size_t first, size_t count)
-{
-  const bool success = c.Validate(type, maxAllowed, first, count);
-  ASSERT_TRUE(success == expectSuccess);
-}
-
-template<typename T>
-void
-CheckValidateOneTypeVariousBounds(mozilla::WebGLElementArrayCache& c, size_t firstByte,
-                                  size_t countBytes)
-{
-  size_t first = firstByte / sizeof(T);
-  size_t count = countBytes / sizeof(T);
-
-  GLenum type = GLType<T>();
-
-  T max = 0;
-  for (size_t i = 0; i < count; i++)
-    if (c.Element<T>(first + i) > max)
-      max = c.Element<T>(first + i);
-
-  CheckValidate(true, c, type, max, first, count);
-  CheckValidate(true, c, type, T(-1), first, count);
-  if (T(max + 1)) CheckValidate(true, c, type, T(max + 1), first, count);
-  if (max > 0) {
-    CheckValidate(false, c, type, max - 1, first, count);
-    CheckValidate(false, c, type, 0, first, count);
-  }
-}
-
-void CheckValidateAllTypes(mozilla::WebGLElementArrayCache& c, size_t firstByte,
-                           size_t countBytes)
-{
-  CheckValidateOneTypeVariousBounds<uint8_t>(c, firstByte, countBytes);
-  CheckValidateOneTypeVariousBounds<uint16_t>(c, firstByte, countBytes);
-  CheckValidateOneTypeVariousBounds<uint32_t>(c, firstByte, countBytes);
-}
-
-template<typename T>
-void
-CheckSanity()
-{
-  const size_t numElems = 64; // should be significantly larger than tree leaf size to
-                        // ensure we exercise some nontrivial tree-walking
-  T data[numElems] = {1,0,3,1,2,6,5,4}; // intentionally specify only 8 elements for now
-  size_t numBytes = numElems * sizeof(T);
-  ASSERT_TRUE(numBytes == sizeof(data));
-
-  GLenum type = GLType<T>();
-
-  mozilla::WebGLElementArrayCache c;
-  c.BufferData(data, numBytes);
-  CheckValidate(true,  c, type, 6, 0, 8);
-  CheckValidate(false, c, type, 5, 0, 8);
-  CheckValidate(true,  c, type, 3, 0, 3);
-  CheckValidate(false, c, type, 2, 0, 3);
-  CheckValidate(true,  c, type, 6, 2, 4);
-  CheckValidate(false, c, type, 5, 2, 4);
-
-  c.BufferSubData(5*sizeof(T), data, sizeof(T));
-  CheckValidate(true,  c, type, 5, 0, 8);
-  CheckValidate(false, c, type, 4, 0, 8);
-
-  // now test a somewhat larger size to ensure we exceed the size of a tree leaf
-  for(size_t i = 0; i < numElems; i++)
-    data[i] = numElems - i;
-  c.BufferData(data, numBytes);
-  CheckValidate(true,  c, type, numElems,     0, numElems);
-  CheckValidate(false, c, type, numElems - 1, 0, numElems);
-
-  ASSERT_TRUE(numElems > 10);
-  CheckValidate(true,  c, type, numElems - 10, 10, numElems - 10);
-  CheckValidate(false, c, type, numElems - 11, 10, numElems - 10);
-}
-
-template<typename T>
-void
-CheckUintOverflow()
-{
-  // This test is only for integer types smaller than uint32_t
-  static_assert(sizeof(T) < sizeof(uint32_t), "This test is only for integer types \
-                smaller than uint32_t");
-
-  const size_t numElems = 64; // should be significantly larger than tree leaf size to
-                              // ensure we exercise some nontrivial tree-walking
-  T data[numElems];
-  size_t numBytes = numElems * sizeof(T);
-  ASSERT_TRUE(numBytes == sizeof(data));
-
-  GLenum type = GLType<T>();
-
-  mozilla::WebGLElementArrayCache c;
-
-  for(size_t i = 0; i < numElems; i++)
-    data[i] = numElems - i;
-  c.BufferData(data, numBytes);
-
-  // bug 825205
-  uint32_t bigValWrappingToZero = uint32_t(T(-1)) + 1;
-  CheckValidate(true,  c, type, bigValWrappingToZero,     0, numElems);
-  CheckValidate(true,  c, type, bigValWrappingToZero - 1, 0, numElems);
-  CheckValidate(false, c, type,                        0, 0, numElems);
-}
-
-TEST(WebGLElementArrayCache, Test)
-{
-  srand(0); // do not want a random seed here.
-
-  CheckSanity<uint8_t>();
-  CheckSanity<uint16_t>();
-  CheckSanity<uint32_t>();
-
-  CheckUintOverflow<uint8_t>();
-  CheckUintOverflow<uint16_t>();
-
-  nsTArray<uint8_t> v, vsub;
-  mozilla::WebGLElementArrayCache b;
-
-  for (int maxBufferSize = 1; maxBufferSize <= 4096; maxBufferSize *= 2) {
-    // See bug 800612. We originally had | repeat = min(maxBufferSize, 20) |
-    // and a real bug was only caught on Windows and not on Linux due to rand()
-    // producing different values. In that case, the minimum value by which to replace
-    // this 20 to reproduce the bug on Linux, was 25. Replacing it with 64 should give
-    // us some comfort margin.
-    int repeat = std::min(maxBufferSize, 64);
-    for (int i = 0; i < repeat; i++) {
-      size_t size = RandomInteger<size_t>(0, maxBufferSize);
-      MakeRandomVector(v, size);
-      b.BufferData(v.Elements(), size);
-      CheckValidateAllTypes(b, 0, size);
-
-      for (int j = 0; j < 16; j++) {
-        for (int bufferSubDataCalls = 1; bufferSubDataCalls <= 8; bufferSubDataCalls *= 2) {
-          for (int validateCalls = 1; validateCalls <= 8; validateCalls *= 2) {
-
-            size_t offset = 0, subsize = 0;
-
-            for (int k = 0; k < bufferSubDataCalls; k++) {
-              offset = RandomInteger<size_t>(0, size);
-              subsize = RandomInteger<size_t>(0, size - offset);
-              MakeRandomVector(vsub, subsize);
-              b.BufferSubData(offset, vsub.Elements(), subsize);
-            }
-
-            for (int k = 0; k < validateCalls; k++) {
-              offset = RandomInteger<size_t>(0, size);
-              subsize = RandomInteger<size_t>(0, size - offset);
-              CheckValidateAllTypes(b, offset, subsize);
-            }
-          } // validateCalls
-        } // bufferSubDataCalls
-      } // j
-    } // i
-  } // maxBufferSize
-}
-
diff --git a/dom/canvas/gtest/moz.build b/dom/canvas/gtest/moz.build
index dcebc4a5e4ef..db5da92baf9e 100644
--- a/dom/canvas/gtest/moz.build
+++ b/dom/canvas/gtest/moz.build
@@ -7,12 +7,8 @@
 with Files('**'):
     BUG_COMPONENT = ('Core', 'Canvas: 2D')
 
-with Files('*WebGL*'):
-    BUG_COMPONENT = ('Core', 'Canvas: WebGL')
-
 UNIFIED_SOURCES += [
     'TestImageBitmapColorUtils.cpp',
-    'TestWebGLElementArrayCache.cpp',
 ]
 
 LOCAL_INCLUDES += [
diff --git a/dom/canvas/moz.build b/dom/canvas/moz.build
index 112a906a4724..fa2315356c8e 100644
--- a/dom/canvas/moz.build
+++ b/dom/canvas/moz.build
@@ -125,7 +125,6 @@ UNIFIED_SOURCES += [
     'WebGLContextValidate.cpp',
     'WebGLContextVertexArray.cpp',
     'WebGLContextVertices.cpp',
-    'WebGLElementArrayCache.cpp',
     'WebGLExtensionBase.cpp',
     'WebGLExtensionBlendMinMax.cpp',
     'WebGLExtensionColorBufferFloat.cpp',
diff --git a/dom/canvas/test/webgl-conf/generated-mochitest.ini b/dom/canvas/test/webgl-conf/generated-mochitest.ini
index c26475abcde8..1dc4d5aeb596 100644
--- a/dom/canvas/test/webgl-conf/generated-mochitest.ini
+++ b/dom/canvas/test/webgl-conf/generated-mochitest.ini
@@ -4958,7 +4958,6 @@ skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance2__rendering__draw-buffers.html]
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance2__rendering__element-index-uint.html]
-fail-if = (os != 'win')
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance2__rendering__framebuffer-completeness-unaffected.html]
 skip-if = (os == 'android' || os == 'linux')
@@ -6125,19 +6124,16 @@ skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__buffers__element-array-buffer-delete-recreate.html]
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__buffers__index-validation-copies-indices.html]
-fail-if = (os != 'win')
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__buffers__index-validation-crash-with-buffer-sub-data.html]
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__buffers__index-validation-large-buffer.html]
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__buffers__index-validation-verifies-too-many-indices.html]
-fail-if = (os != 'win')
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__buffers__index-validation-with-resized-buffer.html]
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__buffers__index-validation.html]
-fail-if = (os != 'win')
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__canvas__buffer-offscreen-test.html]
 skip-if = (os == 'android' || os == 'linux')
@@ -7259,7 +7255,6 @@ skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__rendering__draw-arrays-out-of-bounds.html]
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__rendering__draw-elements-out-of-bounds.html]
-fail-if = (os != 'win')
 skip-if = (os == 'android' || os == 'linux')
 [generated/test_2_conformance__rendering__draw-with-changing-start-vertex-bug.html]
 skip-if = (os == 'android' || os == 'linux')
diff --git a/dom/canvas/test/webgl-conf/mochitest-errata.ini b/dom/canvas/test/webgl-conf/mochitest-errata.ini
index 632b7cada02e..8bba34bc62e3 100644
--- a/dom/canvas/test/webgl-conf/mochitest-errata.ini
+++ b/dom/canvas/test/webgl-conf/mochitest-errata.ini
@@ -71,20 +71,6 @@ skip-if = (os == 'android') || (os == 'linux') || (os == 'win')
 # Timeout on D3D11
 skip-if = (os == 'win')
 
-####################
-# Tests expect conservative index validation, which we skip on WebGL 2.
-# ANGLE still provides it though, so they pass on windows.
-[generated/test_2_conformance__rendering__draw-elements-out-of-bounds.html]
-fail-if = (os != 'win')
-[generated/test_2_conformance__buffers__index-validation-copies-indices.html]
-fail-if = (os != 'win')
-[generated/test_2_conformance__buffers__index-validation.html]
-fail-if = (os != 'win')
-[generated/test_2_conformance__buffers__index-validation-verifies-too-many-indices.html]
-fail-if = (os != 'win')
-[generated/test_2_conformance2__rendering__element-index-uint.html]
-fail-if = (os != 'win')
-
 ########################################################################
 # Complicated