Can’t delete firefox cache when using SDM

Hi everyone;
I use SDM to connect to router and firefox is default web browser. First time I’m asked to enter username and password to connect to router; then I login the SDM configuration interface. After I close the all firefox windows and use SDM to reconnect to the router and I’m not asked to enter user+pass and login the SDM configuration interface (even or not clear the recent cache in firefox option).
I think that’s a security problem. Is there any solution ?! Thanks in advanced for response.