How to switch back Yahoo! Mail to classic version (2) permanently

The following step need to modify Browser User Agent, and its done on Firefox browser.

1. Download and install Mozilla Firefox “User Agent Switcher” plug-in from https://addons.mozilla.org/en-US/firefox/addon/user-agent-switcher/
2. Create new User Agent, for example I created new “Nokia E71″ Browser user agent which this user agent is not supported by New Yahoo Mail interface.

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http://supriyatna.wordpress.com/2011/08/04/how-to-switch-back-yahoo-mail-to-classic-version-2/