Fix last commit.

common/content/hints.js

@@ -276,9 +276,11 @@ function Hints() //{{{
     // the containing block offsets with respect to the viewport
     function getContainerOffsets(doc)
     {
+        let body = doc.body || doc.documentElement;
+
         if (/^(absolute|fixed|relative)$/.test(util.computedStyle(body)["position"]))
         {
-            let bodyRect = (doc.body || doc.documentElement).getClientRects()[0];
+            let bodyRect = body.getClientRects()[0];
             return [-bodyRect.left, -bodyRect.top];
         }
         else