Why is Yahoo Email trying to force me to use only Firefox, Google Chrome, or Internet Explorer?

Update: Message I got when I tried to log in: Yahoo recommends you upgrade your browser to enjoy all the features in the new Yahoo Mail. Google Chrome Firefox Internet Explorer Continue using Classic Mail. You should plan on upgrading your browser soon. "Try it later" - button doesn't work Using another... show more Message I got when I tried to log in:
Yahoo recommends you upgrade your browser to enjoy all the features in the new Yahoo Mail.
Google Chrome
Firefox
Internet Explorer
Continue using Classic Mail.
You should plan on upgrading your browser soon.
"Try it later" - button doesn't work

Using another browser another message:

Javascript is not enabled on your browser.
Enable javascript to enjoy all the features in Yahoo Mail.
Help pages
"Go to Classic Mail" - button doesn't work
4 answers 4