Ouch! Sorry again, Dynamix. First time in 71 years I've heard "Fully-fledged." "Full-blown" is another common synonym. They mean fully developed; full rank; full status. My American Heritage Dictionary lists "full-fledged / -blown" but not "fully-fledged / -blown." Must be pondial, as GG says. It's applied to anything which is not reduced in some way or in an early stage of development. I should think if the web site were typical, full(y)-fledged would apply, although I'm not sure of an example of a web site with fractional status. I expect a full(y)-fledged "conference web site" would be capable of supporting a full(y)-fledged conference.
The expression derives from fully developed bird plumage.
I'm wondering now if UK also uses "fully-blown." (from "in full blossom")
Edit. Feebs, We use a hyphen on this side. I notice you did not. Is that typical?