Firefox 15.01 with the Norton Toolbar which came with NIS v20.1.1.2 is much, much too slow. Login to community dot norton dot com covered more than 1 minute from click on the stored login item to being at the loaded page logged in. Browsing to other sites is also slower than normal.
System: laptop with Windows XP sp3, Firefox v15.01, NIS v20.1.1.2, Celeron 2.0 GHz, 512 MB RAM; wireless internet connection. Firefox on system has search bar, bookmarks toolbar, and norton toolbar, and none else.