In Debian/LMDE, in order to browse samba shares with your firewall active, you must edit /etc/default/ufw and change the following line as follows:

IPT_MODULES="nf_conntrack_netbios_ns"

Then add to your /etc/rc.local file the following command:

echo 1 > /proc/sys/net/netfilter/nf_conntrack_helper

If you don't have a rc.local service active and enabled you can take a look at this post:

Enable /etc/rc.local in Debian