--- a/toolkit/modules/FinderHighlighter.jsm
+++ b/toolkit/modules/FinderHighlighter.jsm
@@ -625,24 +625,24 @@ FinderHighlighter.prototype = {
     // First we'll try without flushing layout, because it's way faster.
     let dwu = this._getDWU(window);
     let { width, height } = dwu.getRootBounds();
 
     if (!width || !height) {
       // We need a flush after all :'(
       width = window.innerWidth + window.scrollMaxX - window.scrollMinX;
       height = window.innerHeight + window.scrollMaxY - window.scrollMinY;
+
+      let scrollbarHeight = {};
+      let scrollbarWidth = {};
+      dwu.getScrollbarSize(false, scrollbarWidth, scrollbarHeight);
+      width -= scrollbarWidth.value;
+      height -= scrollbarHeight.value;
     }
 
-    let scrollbarHeight = {};
-    let scrollbarWidth = {};
-    dwu.getScrollbarSize(false, scrollbarWidth, scrollbarHeight);
-    width -= scrollbarWidth.value;
-    height -= scrollbarHeight.value;
-
     return { width, height };
   },
 
   /**
    * Utility; fetch the current text contents of a given range.
    *
    * @param  {nsIDOMRange} range Range object to extract the contents from.
    * @return {Array} Snippets of text.