I have not tested it in firefox, but sometimes when I click a specific tab it does not take me to the tab. It just dosen't do anything. Then I have to right click and press open in new tab to go to that tab.
I guess you've experienced this on styles that have menu dropdowns activatable on tab hover? Quite often developers make an element that controls dropdown activation (.SplitCtrl) to cover full tab width and you can't click a link behind this element. XenForo has a small delay before dropdowns activate and .SplitCtrl element is only hidden when dropdown menu is active, so you can't click a link instantly and have to wait for menu to activate. This is actually quite easy fixable with reassigning some mouseover and mouseout events, but it should be done on the style developer side. Here is a working example: