Thanks, but I do not want to set a limited list of sites. I want to filter code on web pages. I would like a filter that can take the link visited code and change it to nonvisited, for instance.
Not quite sure what the filter is you are describing? But most browsers can change the colors of links, visited or not. Try Firefox for the browser with the best customizability.
Have you never heard of filtering code on web pages or in other files that go along with them in order to remove or modify code that you do not like?
This is what I want to change: "It's possible for websites to effectively query Firefox's viewing history by using :visited in CSS."
I just don't understand what you want to filter and why? Firefox can filter out whatever you want to filter, including CSS. By 'filter' do you mean 'reveal' so you can see a site's CSS code? Please clarify.
If you are worried about someone tracking your web browsing through CSS tags you've viewed, I would suggest using NoScript (extension through Firefox) and denying cookies set by websites. Also, have your browser clear your browsing history every time you close it.
By filter, I mean alter the code before passing it on to the browser. For instance, if Google wants to see if I visited Yahoo, it could use that code ":visited" to check that. If I change ":visited" to ":nonvisited" before sending the file to the browser, the site would not be able to tell that I had visited whatever site they were checking.