I've never understood why the text/csv mime-type is not recognised by browsers: you should be able to embed a CSV into a HTML page using the <object> elements, much like an image. Then the browser could handle things like fixed headers etc.
It's not too hard to embed it yourself; here's a quick proposal I did when the idea of embedding CSV in a custom element was being discussed on the WHATWG list: http://ephemera.continuation.org/csv.html
The issue of fixed headers is a styling issue, not an issue of what embedding types are supported; and that is solved by the "position: sticky" CSS attribute that this link discusses. There has been an experimental WebKit implementation of this for a while, this now adds an experimental Gecko implementation. Hopefully this will be standardized soon and available in non-experimental form.
