Visited links should be working, I don't notice anything wrong with that per se. It might be that the browser is just busy managing all the new history in the background, maybe even awaiting a restart.

I won't be spending time to work out if it does or does not work in waterfox classic. It's more than likely the addon is using features just not available in that browser.

I added a description, I shouldn't have been lazy to begin with :)
If you have any notes on the description let me know and I could change it.

Thanks for the review!