Firefox Add-on -- NIS vs. Norton Security

I currently have NIS 22.5.5.15, Windows 7.

For almost a year, the Norton Toolbar / Identity Safe add-on has caused problems for me with Firefox (always the latest version of both FF and the Norton add-on).  The symptom is that after browsing awhile with the add-on enabled, FF becomes sluggish, e.g. scrolling is delayed and choppy.  With the add-on disabled, I do not encounter FF sluggishness.  The problem persisted even when I tried temporarily disabling all my other FF add-ons in case one of them was conflicting with the Norton add-on.  So I keep the Norton add-on disabled most of the time, even though I wish I didn't have to do that.  

My question:  Is there any reason to believe this problem will likely resolve if I either (1) switch from NIS to Norton Security, or (2) do a *full* uninstall-reinstall of NIS?  (It would be much easier for me to do an NIS full uninstall-reinstall than to do a Firefox [plus add-ons] reset/recover/reconfigure.)