Cookies do not expire (Flight Recorder)
Flight Recorder guesses the path for 'client side' cookies (and if multiple cookies have the same name, they are al assigned the same path, and we only remember one of them). Maybe add JS interface so these cookies are set before every request they are sent with?
Real browsers are multithreaded but Flight Recorder serialises all requests and they are run from a single thread
Cookie: before Host: header will cause Flight Recorder problems (never seen it happen though)