Problem when downloading POP's from Standard Bank Online [continued]

Using downloading from eg. an email, when download is selected a NEW TAB is added to the right of the email tab in the Firefox Web Browser for eg. the .pdf file being downloaded. When the download is completed this new tab is clicked to exit the display of the .pdf file presented when 'download' is selected, thus returning to the original screen from which 'download' was selected. THIS WORKS WELL.
HOWEVER
Using the Standard Bank Online facility:
When I try to download a POP from the transactions/History/Proof of payments, a NEW NEW TAB IS NOT ADDED TO THE RIGHT IN THE FIREFOX WEB BROWSER RATHER THE STANDARD BANK LOGIN TAB IS OVERWRITTEN IN THE FIREFOX WEB BROWSER. THEN ON CLICKING THIS TAB TO EXIT THE EG. PDF DISPLAY SCREEN, THE STANDARD BANK LOGIN IS ABORTED ENTIRELY.
How do I exit the download file displayed without aborting the Standard Bank Login?