Mark all visited links as custom color.
In Visited.
Try clear your Site Exceptions in Visited config.
Sample: http://i.imgur.com/joWUBLD.png
If you want to use Site Exceptions. You need to edit Visited Lite after install it.
I had cleared the site exceptions first.
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Subsequent to my post (above) for the first time ever in many years, Firefox would not load, so I loaded it in its Safe Mode, and removed GreaseMonkey. Now both Firefox and Visited work fine.
Only partially fixes Visited in Firefox 43.0.2
With this script installed visited links now change color--but not the color I chose. The color picker provided with Visited is useless.