One other other differences between regular and private windows, besides cached files, are cookies. You can clear cookies for an individual site this way:

While viewing a page on the site, click the lock icon at the left end of the address bar. After a moment, a "Clear Cookies and Site Data" button should appear at the bottom. Go ahead and click that. Firefox will ask you to confirm; go ahead and confirm.

Then try reloading the page -- presumably you will then need to log in again.

Does that help?

It's also possible that one or more of your add-ons are not running in private windows. More info on that in the following article: Extensions in Private Browsing. If you suspect that one of your add-ons is breaking that page, you could consider disabling it completely so that it doesn't run in regular windows, either.

Thank you for you reply. Did all that you suggested with no success...when you speak of extensions I believe I only have one and its an ad blocker...

Ha....you are right...I disabled the extension ad blocker in regular firefox and the page showed up...when I enabled the ad blocker the page went away. Thank you for your help...I believe the issue is resolved.

Ad blockers use filters that target various patterns in pages, so it's possible that one of the filters is having unintended consequences. You often can use the ad blocker's toolbar button to allow ads on the site, or adjust its settings in other ways so that you can continue to benefit from it on other pages. Or you could look for a different one that creates fewer issues.