I could not even post comments to my own yahoo group. I figured it was Safari, since the last build has been rather buggy, but I encountered the same problem with Firefox. It all probably works just fine with Micro-phallus Internet Exploder, but frankly I'd rather give up access to my yahoo group
I finally did get everything to work in Firefox, but I suspect it is only a matter of time before yahoo gets dissolved completely, as the Borg adds Yahoo's uniqueness to its own.
If you have a email account with Yahoo, I recommend downloading anything you care about such as your contacts and important emails. Then go with gmail or some other service.