Do you think that the New Yahoo mail sucks ? And you can't find a way to return to the old Classic Mail version ? Well here's what I found searching the web:
To go back to YAHOO! MAIL CLASSIC...
For IE: Open TOOLS > INTERNET OPTIONS >> SECURITY. In security click "CUSTOM LEVEL" -> disable active scripting in the scripting section.
2) Go and login to your Yahoo mail account.
Bellow the warning there is two options, click the second (PERMANENT) to switch back to YAHOO! Classic. DO NOT click the first one "ONE TIME ONLY" option.
Thanks to RUDJAKE a yahoo answer member.