DOCSIS is a cable modem protocol. It is not used on FiOS in any way, shape or form.
FiOS uses MoCA or Ehthernet for the ONT to router connection.
Verizon FIOS services does not use a modem. There is either an ethernet or coax connection from the Verizon Network into the home. If ethernet you can plug any router you want into that connection. If coax you would need to use a router that supports coax or ask VZ to see about converting your connection from COAX to Ethernet.
Also, if you have FIOS TV Services you may want to stick with the VZ provided router. The VZ Router provides Internet Connectivity to the STB's for On-Demand, Channel Guide and remote programming of your DVR.
Some folks will install a secondary router leaving the STB's connected on the VZ Router and having all of your devices connected on the secondary router including wireless LAN