Scroll-down stops before the end of my index page's source code, preventing me from editing.

My summary says it all, really. There's not much more that I can add, except that I have used Firefox for many years and have never had this problem before. The index page itself is fine when I view it in Firefox. And if I right-click the page and view its source code, everything is there. Furthermore, I have no difficulty in editing the page in other browsers. (Since this problem arose, I have been using the Norton browser. But I have also been able to scroll down to the end of the source code in Google Chrome.)