Manual login process prompts for mobile number as follows:
"Protect your account
Add a mobile number to better protect your account. Yahoo! will send you
recovery information if you forget your password or become locked out of your
account. Yahoo! will also use this mobile number to help defend against hackers
who may have stolen your password, by sending a security code that you can use
to unlock your account. It
is important to keep this information up to date.
[Remind Me Later button]"
Pressing [Save and Continue button] without adding phone number goes directly to email inbox without problems.
Error Console:
HttpComms3.js: send : Exception : NS_ERROR_INVALID_POINTER.
Error message: Component returned failure code: 0x80004003 (NS_ERROR_INVALID_POINTER) [nsIIOService.newChannelFromURI]
345
YahooPOPBETA.js: loginHandler : Exception : Error.
Error message: httpConnection returned false
299
Let me know if you need more details.