firefox asks every time for personal certificate. it wont remember choice.

I have 2 personal certificates for accessing several secure sites. If I check to remember choice, Firefox remembers choosen certificate and works until I close Firefox completely. When I open Firefox it chooses wrong certificate (it always chooses first certificate on list). If I choose ask every time and I select certificate and check "remember choice" it remembers until I restart Firefox. Aftert restarting it asks again( this site has requested that you identify yourself with a certificate). I have reset firefox and imported certificates, and still same happens. It happens on several versions of firefox and on my all computers. How to remember which certificate to choose on one specific web page? Thank you