Are you receiving a reminder form Yahoo to upgrade your Opera every time you login to Yahoo Mail?
First, try going to this link and installing the latest version of Opera:
Download Opera for computers - Opera Software
If that does not work, to fix this problem you'll need to trick Yahoo Mail into thinking that your Opera is Firefox.
To change your User Agent and make Yahoo think you're using Firefox download and install this plugin:
https://addons.opera.com/en/extensions/details/user-agent-switcher/
Restart Opera, then change your user agent to Firefox:
Try logging in at mail.yahoo.com
If Yahoo Mail thinks your Firefox is too old you'll need to update the Firefox user agent.
Go to the Opera menu and select Extensions (or keyboard Control+Shift+E):
Click the Options button:
Select the Firefox group and click Edit next to Firefox for Windows:
Replace the string listed with:
Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:25.0) Gecko/20100101 Firefox/25.0
Click Save.
Open a new tab and go to http://mail.yahoo.com
First, try going to this link and installing the latest version of Opera:
Download Opera for computers - Opera Software
If that does not work, to fix this problem you'll need to trick Yahoo Mail into thinking that your Opera is Firefox.
To change your User Agent and make Yahoo think you're using Firefox download and install this plugin:
https://addons.opera.com/en/extensions/details/user-agent-switcher/
Restart Opera, then change your user agent to Firefox:
Try logging in at mail.yahoo.com
If Yahoo Mail thinks your Firefox is too old you'll need to update the Firefox user agent.
Go to the Opera menu and select Extensions (or keyboard Control+Shift+E):
Click the Options button:
Select the Firefox group and click Edit next to Firefox for Windows:
Replace the string listed with:
Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:25.0) Gecko/20100101 Firefox/25.0
Click Save.
Open a new tab and go to http://mail.yahoo.com