No need for an extension, in about:config you can toggle network.http.SendRefererHeader from the default value of '2' to '0', which will disable all referer headers.
Some websites require the referrer to work; RefControl allows you whitelist exceptions, and also configure a few different options.
As far as sites which require a referrer header, it has been my experience that these are very few and far between. I get one occasionally and if the content is worthy, I'll briefly disable then re-enable my setting.
Not for everyone, I know, but it works well for me.