Hi, Firefox doesn't have any built-in features to increase colorfulness or contrast (except themes for the toolbars). Mozilla has a product suggestion site at https://connect.mozilla.org/. If you have time, I think it would be a good idea to post this request there to get into the current feedback stream. Use the "Ideas" section of the site (at https://connect.mozilla.org/t5/ideas/idb-p/ideas).