You can easily do that browser-side. There are helper tools for this, too. Like stylebot for Chrome. In Firefox the usual way is just to create a userContent.

You can easily do that browser-side. There are helper tools for this, too. Like stylebot for Chrome. In Firefox the usual way is just to create a userContent.css in your profile folder, then add sections like this: @-moz-document domain(whatever_domain.com) { // your site-specific css comes here, use !important for overrides }