Serious question.
Suppose one has been asked to leave one's firm for bad performance. If the recruiter asks why you are looking for a new firm, do you tell her the truth? Or make something up?
By statutes in most states, you can demand to see your personnel record. I know in my state, if you make a written request to access your record either during or up to one year after the termination of your employment, your employer must either grant you access and a copier (i'd recommend bringing a good camera just in case), or make copies for you. Law firms are no exception. And they will comply because the penalty is on the order of $500 (if i recall correctly) and a potential investigation by your state's labor department.
Once you get your file, you will know exactly what the said about you and you can frame your answer accordingly. Yeah, my performance dipped during February 2009, which incidently corresponded with the crash of the market, the de-equitizing of 10 partners, the firing of 50 other people, the drop in profits of $X per partner, etc. Frame the facts in a way that's really favorable to you without being a turnoff to your potential employer. You're an attorney - you'll figure out how to walk that really fine line after some practice run-throughs (being careful to not go on a diatribe like DogDayPM mentioned above).
As a final note, don't worry too much about this as it is likely out of your control. Absent some egregious record, your interviewer will know your "performance" is all pretext. Whether they want to acknowledge it is beyond your control. In fact, they are probably doing the same thing. Just put your bet foot forward, bury the hatchet, but try not to lie down completely. Either your interviewer will understand or they won't - but that will likely be determined long before you step into that room.
Good luck man