--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -1352,16 +1352,35 @@ CanvasRenderingContext2D::ClearTarget()
   mDSPathBuilder = nullptr;
 
   ContextState *state = mStyleStack.AppendElement();
   state->globalAlpha = 1.0;
 
   state->colorStyles[Style::FILL] = NS_RGB(0,0,0);
   state->colorStyles[Style::STROKE] = NS_RGB(0,0,0);
   state->shadowColor = NS_RGBA(0,0,0,0);
+
+  // For vertical writing-mode, unless text-orientation is sideways,
+  // we'll modify the initial value of textBaseline to 'middle'.
+  nsRefPtr<nsStyleContext> canvasStyle;
+  if (mCanvasElement && mCanvasElement->IsInDoc()) {
+    nsCOMPtr<nsIPresShell> presShell = GetPresShell();
+    if (presShell) {
+      canvasStyle =
+        nsComputedDOMStyle::GetStyleContextForElement(mCanvasElement,
+                                                      nullptr,
+                                                      presShell);
+      if (canvasStyle) {
+        WritingMode wm(canvasStyle);
+        if (wm.IsVertical() && !wm.IsSideways()) {
+          state->textBaseline = TextBaseline::MIDDLE;
+        }
+      }
+    }
+  }
 }
 
 NS_IMETHODIMP
 CanvasRenderingContext2D::InitializeWithSurface(nsIDocShell *shell,
                                                 gfxASurface *surface,
                                                 int32_t width,
                                                 int32_t height)
 {