Re: Verizon Fios and Belkin Router
First off, reset the Belkin router to factory defaults.
Next, configure the Belkin router for a static WAN address outside the range of the Actiontec DHCP address pool, but in the same subnet. I use 192.168.1.253 on my Actiontec for the DMZ host and use the same address on the attached router, in my case I have a ZyXEL NBG-415N as the secondary router.
Finally, go into the Actiontec MI424WR and configure the connection to the Belkin to be in the DMZ of the Actiontec using the static WAN address. Normally, the Belkin is at 192.168.2.x for it's LAN subnet, which will work fine. If it happens to be at 192.168.1.x on the LAN side, you'll have to change that subnet to something other than 192.168.1.x to avoid a WAN/LAN subnet issue.
If you only have FiOS Internet, you can dispense with the Actiontec router and use your Belkin connected directly to the ONT. If you have the TV service as well, the Actiontec supplies the program guide and on-demand functions, so that isn't an option.