Looking for a Firefox add-on that will always override the css rules

There are some pages that I visit very often and it would be nice if I could do some small tweaks to make them more useful for me. I can do that with Firebug, but they get reset when the page is refreshed or if I go to a different page. What I would like is an add-on that can always look for a certain element and always apply a rule to it. For instance, I could say div#annoyingred {color: black;}

Thanks!

Not sure if this is or isnt what your looking for, https://addons.mozilla.org/en-US/firefox/addon/6510

Found it looking for a textarea find and replace.

It's not really, but it might come in handy, thanks! After a bit more looking around, I found Stylish (https://addons.mozilla.org/en-US/firefox/addon/2108) but I haven't had time to try it out yet, so if you know of a better one, please let me know.