OWA displaying only 25 emails in folder

Using Firefox on Mac (OS 10.6.8) to work with OWA. Intermittently when displaying emails from a folder (In this case, the inbox), a maximum of 25 emails are displayed.  Scrolling down, results only in white space.  Resorting will work but it only displays the top 25 item based on the new sort.  Searching only seems to search through the items that are displayed.  We have fewer than 200 emails in the folder.

Any ideas why this might be happening?  And how it might be fixed?

Thank you.

Bob Oxford