Every time I load my Firefox browser (which has X-notifier) and load Yahoo Mail, it loads fine.
But when I go to view and delete an e-mail, the browser goes to the Yahoo Mail log in page. If I simply go back to the e-mail and delete again, it's fine... but it's quite annoying to have to do that every time I open my Firefox browser.
Working for me
Any changes recently? Firefox install or update... X-Notifier install or update? Other addons?
Sounds like a corruption, or conflict. Maybe try clearing cache and cookies.
By the way, loading software is when you install it, generally... (when you start a program, it does load into RAM memory though).
After you start Firefox, are you starting your yahoo mail session via X-Notifier or by manually opening a tab and going to yahoo... or something else?
I have the latest versions of FF and X-N and no problems with yahoo mail or deleting an email there.
I do use X-Notifier to start up Yahoo Mail. (Although I skip the OATH prompt.)