What is the model of the camera?
I dont use Firefox but my regular process is
Setup the motion /smart event for the frame captures in >> Events >>
format the card.
also to have the camera record until capacity and then overwrite the oldest footage, make sure you have Overwrite checked under Configuration >> Storage >> Schedule Settings >> Record Schedule >> Advanced
You might also want to check the capacity and free space of your microSD card under Configuration >> Storage >> Storage Management >> HDD Management and just double-check everything is as it should be. Whilst you're there, just make sure the Quota settings are set to something appropriate too - 25% for picture and 75% for record is default.