--- a/editor/libeditor/html/nsHTMLCSSUtils.cpp
+++ b/editor/libeditor/html/nsHTMLCSSUtils.cpp
@@ -637,17 +637,16 @@ nsHTMLCSSUtils::GetComputedStyle(nsIDOME
 }
 
 already_AddRefed<nsComputedDOMStyle>
 nsHTMLCSSUtils::GetComputedStyle(dom::Element* aElement)
 {
   MOZ_ASSERT(aElement);
 
   nsIDocument* doc = aElement->GetCurrentDoc();
-  NS_ASSERTION(doc, "Trying to compute style of detached element");
   NS_ENSURE_TRUE(doc, nullptr);
 
   nsIPresShell* presShell = doc->GetShell();
   NS_ASSERTION(presShell, "Trying to compute style without PresShell");
   NS_ENSURE_TRUE(presShell, nullptr);
 
   nsRefPtr<nsComputedDOMStyle> style =
     NS_NewComputedDOMStyle(aElement, EmptyString(), presShell);