Opera Browser need help with tabs

[1Cheap2Crazy]

I'm trying out Opera, but I can't get links to open in a new tab when I click on them with my mouse wheel(middle button). Instead a new window opens. Under tabs the only item I have checked is "Show close button on each tab".

Thanks

 

[AllGoodNamesAreTaken]

Tools->Preferences->Advanced->Shortcuts->Middle Click Options