When using Thebes, we need to Flush the surface before drawing directly to the surface with GDI.

widget/src/windows/nsNativeThemeWin.cpp

@@ -775,6 +775,9 @@ nsNativeThemeWin::DrawWidgetBackground(nsIRenderingContext* aContext,
 
 #ifdef MOZ_CAIRO_GFX
   gfxContext *ctx = (gfxContext*)aContext->GetNativeGraphicData(nsIRenderingContext::NATIVE_THEBES_CONTEXT);
+
+  ctx->CurrentSurface()->Flush();
+
 #if 0
   gfxMatrix m = ctx->CurrentMatrix();
   XFORM xform;
@@ -1787,6 +1790,11 @@ nsresult nsNativeThemeWin::ClassicDrawWidgetBackground(nsIRenderingContext* aCon
 	nsRect tr(aRect);
 	transformMatrix->TransformCoord(&tr.x,&tr.y,&tr.width,&tr.height);
 #ifdef MOZ_CAIRO_GFX
+  gfxContext *ctx = (gfxContext*)aContext->GetNativeGraphicData(nsIRenderingContext::NATIVE_THEBES_CONTEXT);
+
+  // flush the surface to make sure things are set up right
+  ctx->CurrentSurface()->Flush();
+
   tr.x = NSToCoordRound(tr.x * T2P);
   tr.y = NSToCoordRound(tr.y * T2P);
   tr.width  = NSToCoordRound(tr.width * T2P);
@@ -2086,6 +2094,11 @@ nsresult nsNativeThemeWin::ClassicDrawWidgetBackground(nsIRenderingContext* aCon
       break;
   }
   RestoreDC(hdc, -1);
+
+#ifdef MOZ_CAIRO_GFX
+  ctx->CurrentSurface()->MarkDirty();
+#endif
+
   return rv;
 }