The assert at the end of HTMLSelectElementImpl::selectedIndex fails when no item is selected. It went unnoticed before because it was a Q_ASSERT, but in r12471 it was changed to an ASSERT. Anyway, it is bogus since -1 is the correct value to return when no option is selected.
Created attachment 6119 [details] Remove the assert Not sure the test is necessary
Comment on attachment 6119 [details] Remove the assert r=me
Oops, yes, I was wondering which of the Q_ASSERT that I changed to ASSERT were bogus. Sorry, my mistake.
*** Bug 6974 has been marked as a duplicate of this bug. ***