userstyles.org - Link: Visited links with opacity effect.

To use this style, install Stylish with samfind Bookmarks Bar (or install just Stylish).

(Though installing Stylish is recommended, Greasemonkey users can also install this style as user script.)

To use this style, install Firefox and Stylish.

(Though installing Stylish is recommended, IE7Pro users can also install as a user script.)

To use this style, install Firefox and Stylish.

(Though installing Stylish is recommended, you can also install as plain CSS or install as user JS.)

To use this style, first install Stylish. If you already have Stylish, make sure this site is allowed to run JavaScript.

(Though installing Stylish is recommended, you can also install this style as user script.)