diff --git a/dom/canvas/WebGLContext.cpp b/dom/canvas/WebGLContext.cpp
index b8e9159ca48be..765bf42d6be33 100644
--- a/dom/canvas/WebGLContext.cpp
+++ b/dom/canvas/WebGLContext.cpp
@@ -483,32 +483,46 @@ bool WebGLContext::CreateAndInitGL(
     flags |= gl::CreateContextFlags::REQUIRE_COMPAT_PROFILE;
   }
 
-  switch (mOptions.powerPreference) {
-    case dom::WebGLPowerPreference::Low_power:
-      break;
-
-    case dom::WebGLPowerPreference::High_performance:
-      flags |= gl::CreateContextFlags::HIGH_POWER;
-      break;
+  {
+    bool highPower = false;
+    switch (mOptions.powerPreference) {
+      case dom::WebGLPowerPreference::Low_power:
+        highPower = false;
+        break;
+
+      case dom::WebGLPowerPreference::High_performance:
+        highPower = true;
+        break;
+
+        // Eventually add a heuristic, but for now default to high-performance.
+        // We can even make it dynamic by holding on to a
+        // ForceDiscreteGPUHelperCGL iff we decide it's a high-performance
+        // application:
+        // - Non-trivial canvas size
+        // - Many draw calls
+        // - Same origin with root page (try to stem bleeding from WebGL
+        // ads/trackers)
+      default:
+        highPower = true;
+        if (StaticPrefs::WebGLDefaultLowPower()) {
+          highPower = false;
+        } else if (!mCanvasElement->GetParentNode()) {
+          GenerateWarning(
+              "WebGLContextAttributes.powerPreference: 'default' when <canvas>"
+              " has no parent Element defaults to 'low-power'.");
+          highPower = false;
+        }
+        break;
+    }
 
-      // Eventually add a heuristic, but for now default to high-performance.
-      // We can even make it dynamic by holding on to a
-      // ForceDiscreteGPUHelperCGL iff we decide it's a high-performance
-      // application:
-      // - Non-trivial canvas size
-      // - Many draw calls
-      // - Same origin with root page (try to stem bleeding from WebGL
-      // ads/trackers)
-    default:
-      if (!StaticPrefs::WebGLDefaultLowPower()) {
-        flags |= gl::CreateContextFlags::HIGH_POWER;
-      }
-      break;
-  }
+    // If "Use hardware acceleration when available" option is disabled:
+    if (!gfxConfig::IsEnabled(Feature::HW_COMPOSITING)) {
+      highPower = false;
+    }
 
-  // If "Use hardware acceleration when available" option is disabled:
-  if (!gfxConfig::IsEnabled(Feature::HW_COMPOSITING)) {
-    flags &= ~gl::CreateContextFlags::HIGH_POWER;
+    if (highPower) {
+      flags |= gl::CreateContextFlags::HIGH_POWER;
+    }
   }
 
 #ifdef XP_MACOSX