New Mail Not Pushin to Inbox

I use Firefox to access Zoho Mail and I also have it synced with my Blackberry. When new mail arrives, it shows up immediately on my Blackberry (with an audible notification) and the Zoho tab in Firefox also shows how many new mails have arrived (in parentheses). Since I have a notification Add-On installed in Firefox, I also receive an audible notification.

However, when I open the Zoho tab in Firefox, the new mail is not in my Zoho Mail inbox. I have to use refresh to get the new mail to show up in the inbox.

What's wrong?