Can you help me with my Yahoo Mail inbox problem?

I have Yahoo Mail constantly open in a tab in Firefox. If I delete all the mail from my inbox and then then a new e-mail comes in, it doesn't appear where you would see what the e-mail is. The inbox folder will indicate that there is new mail, but the list of e-mails is blank. If I click onto another folder and then back onto the inbox, the new e-mail now appears. As a temporary solution, I have been leaving one e-mail undeleted, in which case new e-mail shows up in the list without me having to click out of the inbox and back. How can I fix this issue?