I've had this too but think the problem was at Yahoo's end, not Fire's.  When I had this problem I tried using MNS Messenger and it also couldn't connect.

On 22 Mar 2006, at 04:19, fire-talk-request@lists.sourceforge.net wrote:

"Information: There has been an unknown error while logging in to Yahoo."

What unknown error? Has anybody with Mac OS X similar problems and what is

the solution?

Bernhard Bauer