First of all, congratulations on being in such a wonderful position (and trust me, most 1L's out there are envious that not only do you have one paid internship in the hand, there's another out there that's considering you).
I'm a 1L like you, so take what I say from the perspective that this is what I'd be thinking about. I'd first figure out how important the money is to me. If this is really a question about making some money over the summer, then it's probably wise to just take the University job (provided you don't hear from the firm tomorrow).
However, if this is more about what you could possibly see yourself doing in the future and trying to get really good experience, then I'd say maybe you should consider waiting on the firm (have you tried asking the University for an extension?). Here are my reasons for why the firm might be worth the wait: (1) they likely know what to do with their clerks because they've had clerks before and probably will have decent work for you; (2) you're probably more likely to work in a firm after graduation than In-House anywhere; (3) the firm would probably provide good enough contacts that if you did a good job this summer, you'd be able to go back next year, and eventually land a full-time position (this is usually not the case with in-house internships).
Even if the firm doesn't pan out, you have the Federal judge to extern for and that's always great experience.
Do you know how many people are being considered for this firm job? If it's like fifty people for one position, then that's going to be tough; but if it's reasonable, then consider what I said above.
At the end of the day, you want to get experience and maybe learn about where you could see yourself practicing in the future.