My application has 2 rows of tabs when viewed with Ajax. I am unable to open the 1st 2 tabs on the second row using FireFox. I have seen the same problem with other users of the same QVW but on the top row of tabs. Their browser was Safari but I don't know if this is relevant. We are running a SBS with the same issue in both v9 and v10.
Resolved. A transparent object partially covered the tab.