Check this article

http://www.technogadge.com/how-to-switch-back-to-yahoo-mail-classic/

Hi Taz777,

Unfortunately, according to the following help page, it appears that the most recent update of Yahoo! Mail is not reversible:

http://help.yahoo.com/kb/index?locale=en_US&page=content&y=PROD_MAIL_ML&id=SLN4993&impressions=true

If you have further concerns with your Yahoo! Mail, please use the "Get Help" button on the right side of that page.

Thanks!!

- Ralph

I was given a workaround for this problem. It worked for me and I am in Canada. Seems funny to go through the UK to get to a Yahoo.ca email page. I also saw this tip with US instead of the UK in the URL. So it should work with your country code too. Good luck. It does however only work while you are reading and replying to your mail in a particular session, it is not a permanent fix. I made it a bookmark on my Firefox toolbar for convenience.

http://uk.mc598.mail.yahoo.com/mc/launch

Try this link. I worked for me today June 12, 2013

http://mrd.mail.yahoo.com/switchclassic