diff --git a/dom/canvas/WebGL2ContextQueries.cpp b/dom/canvas/WebGL2ContextQueries.cpp
index b3ffe264e6e6..1fec22d70e3d 100644
--- a/dom/canvas/WebGL2ContextQueries.cpp
+++ b/dom/canvas/WebGL2ContextQueries.cpp
@@ -6,6 +6,8 @@
 #include "WebGL2Context.h"
 #include "GLContext.h"
 #include "WebGLQuery.h"
+#include "gfxPrefs.h"
+#include "nsThreadUtils.h"
 
 namespace mozilla {
 
@@ -255,6 +257,7 @@ WebGL2Context::EndQuery(GLenum target)
     }
 
     UpdateBoundQuery(target, nullptr);
+    NS_DispatchToCurrentThread(new WebGLQuery::AvailableRunnable(activeQuery));
 }
 
 already_AddRefed<WebGLQuery>
@@ -325,6 +328,11 @@ WebGL2Context::GetQueryParameter(JSContext*, WebGLQuery* query, GLenum pname,
         return;
     }
 
+    // We must wait for an event loop before the query can be available
+    if (!query->mCanBeAvailable && !gfxPrefs::WebGLImmediateQueries()) {
+        return;
+    }
+
     MakeContextCurrent();
     GLuint returned = 0;
     switch (pname) {
diff --git a/dom/canvas/WebGLQuery.cpp b/dom/canvas/WebGLQuery.cpp
index 016aa198d194..e557b8b4505c 100644
--- a/dom/canvas/WebGLQuery.cpp
+++ b/dom/canvas/WebGLQuery.cpp
@@ -20,6 +20,7 @@ WebGLQuery::WrapObject(JSContext* cx, JS::Handle<JSObject*> givenProto)
 
 WebGLQuery::WebGLQuery(WebGLContext* webgl)
     : WebGLContextBoundObject(webgl)
+    , mCanBeAvailable(false)
     , mGLName(0)
     , mType(0)
 {
diff --git a/dom/canvas/WebGLQuery.h b/dom/canvas/WebGLQuery.h
index 5886a75ed8a5..7f02fb35d7e2 100644
--- a/dom/canvas/WebGLQuery.h
+++ b/dom/canvas/WebGLQuery.h
@@ -10,6 +10,7 @@
 #include "nsWrapperCache.h"
 
 #include "WebGLObjectModel.h"
+#include "nsThreadUtils.h"
 
 namespace mozilla {
 
@@ -22,6 +23,19 @@ class WebGLQuery final
 public:
     explicit WebGLQuery(WebGLContext* webgl);
 
+    class AvailableRunnable final : public nsRunnable
+    {
+    public:
+        AvailableRunnable(WebGLQuery* query) : mQuery(query) { }
+
+        NS_IMETHOD Run() override {
+            mQuery->mCanBeAvailable = true;
+            return NS_OK;
+        }
+    private:
+        const RefPtr<WebGLQuery> mQuery;
+    };
+
     bool IsActive() const;
 
     bool HasEverBeenActive() const {
@@ -42,6 +56,8 @@ public:
     NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(WebGLQuery)
     NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(WebGLQuery)
 
+    // Track whether the event loop has spun
+    bool mCanBeAvailable;
 
 private:
     ~WebGLQuery() {
diff --git a/gfx/thebes/gfxPrefs.h b/gfx/thebes/gfxPrefs.h
index 7bb41fdc8eb9..bde9f242fae0 100644
--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -437,6 +437,7 @@ private:
   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.allow-immediate-queries",         WebGLImmediateQueries, bool, false);
 
   DECL_GFX_PREF(Live, "webgl.webgl2-compat-mode",              WebGL2CompatMode, bool, false);