Turris Omnia something like switch/bridge with firewall

is it possible to configure TO as some transparent device which will be doing firewall (and maybe some other things like LXC containers etc), all other things like routing/vlans/dhcp etc will be done by another router?

Something like:

MODEM (in bridge mode) --> Turris --> router --> LAN

Why do you think you need any special configuration here? As long as you make sure that there are no subnet conflicts (between Turris’ LAN side and your other router’s LAN), then the default configuration will do the trick.

sort of similar question been asked before Turris as firewall only