@Andrew: When its WordPress' own annual release, I hold the free theme to a slightly higher standard, even if it is free.
@esmi: That's fair. But, when options like Enquire.js exist, can sacrificing the theme to that user base still using legacy browsers really be justified?
@mhutchin: Trust me, I am in no way advocating the use of any old browsers, as all of them were retired for a good reason, including both security holes and lacking functionality. That said, in not taking the effort to support as many browsers as possible, the only person being hurt is your employer. The site looking bad in someone's old browser is not going to make them change browsers. If they've stuck with it that long, it will take significantly more for them to change. What it will do is make your employer look bad, which is never a good thing. My two cents, anyway.
The reason this department in my university runs such an old version of FF is because the OS running on the machines, an older Ubuntu install, doesn't support the newer browsers. Though it is undoubtedly something that needs to be updated, it is not a simple resolution. In the academic and corporate world, issues such as this occur all the time. I believe that web developers need to do their best to support as much as they can and not presume that the person using an older browser can be coerced into upgrading, since they often don't have a choice in the matter or are simply too stubborn to have their mind changed.