No, I have no news of a sequel or series continuation. That would have a title name of "ZOMG MY LIFE IS COMPLETE NEW FIREFLY!!!".
No, what we have here is a fan fighting back.
Nathan Fillion, and for everyone who is not a Browncoat, he plays Malcolm "Mal" Reynolds, the captain from the series Firefly and spawning movie Serenity, has a new series coming called Castle, and here is the Wikipedia page...
Located at this page, in the first part...
http://en.wikipedia.org/wiki/Castle_(TV_series)
A fan expresses his dismay at the cancellation of Firefly.
A picture in case the page is edited...
Brilliant.