Johnathan, I was just reading the FF bug progress report you posted. It seems to satisfy the requirement here except we have not had it render correctly in IE under win 7. Any of them other than Chrome actually.
I will solve the issue by removing the entire site and reloading 1.9 and restoring the last BU then deal with the rest as it resolves OK. 1.9 has no problem resolving pages correctly on Win 7/FF4
Very strange stuff indeed.