That will depend on how the router is connected to the ONT and if you have FIOS TV too or not.
Assuming ethernet to ONT and not using FIOS TV too, easy answer bypass that router. And of best interest that would mean behind a router.
The catch to that easy answer to getting online is that they have MAC Bonding which means you will have to power down the old router (the one broken), keep it down for at least two hours before powering up and connecting the new router.
That assumed that you don't know/have a record of what the MAC/Physical/Hardware WAN Address of the old router is, because if you do in your new router you would spoof/clone the MAC/Physical/Hardware WAN Address of the old router.
With one another catch to using a router via ethernet, if you use your own (not FIOS one) they will support you only up to the ONT from their end.
By best interest that would mean behind a router, I can think of two reason. There might be more (so at least the following).
#1 Easier to share the connection considering how many IPv4 Addresses exist vs the number of computers (and even users) that are online.
#2 A level of security. Users from the net can not connect through your router to your computers by default. This assumes that your computers are clean and you not using any kind of remote view/control software (Like Team Viewer).
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