Mail does't open in Preview mode

Mail does't open in Preview mode

On the webmail interface, for my free personal email account, when I click on an email most of the time a New Tab will open and I can the see the email in the Tab. The problem is that I have selected Quickview as the setting for opening an email and not a New Tab. I don't want a New Tab to be opened. Is there another setting I need to select to open a mail message in Preview by default?

I am viewing the webmail interface in Firefox 3.6.15 on Mac OS X 10.6.6

James