Can't access C7100V setup AND can't bypass smart wizard/genie

Summary for everyone who might find this useful:

The initial problem was a C7100V which wouldn't execute the "Wizard"
in a web browser AND which wouldn't allow bypass of the Wizard by using
the URLs listed in the documentation (and here). The router worked, however:
that is, when plugged into a live cable connection it provided Internet,
phone and TV service. So the only issue was that I couldn't configure it.

Lots of testing with different browser/OS combinations got nowhere. Symptoms
didn't change whether it was on a live cable connection or just sitting on
a desk. Finally -- with help from people here -- the solution was:

1. Reset it while it's powered on and hold the button for 30 seconds.
(Page 124 of the manual, document C7100V_UM_EN.pdf, says 7 seconds. That's
apparently not long enough, go for 30 seconds. The lights on the front
will flash at somewhere around 25-30 seconds.)

2. Connect a network cable between the C7100V and your laptop/desktop.
No other connections: no coax on the C7100V, no wifi on your laptop/desktop.

3. Use a brand-new installation of a web browser. I had success with Firefox
on Ubuntu (finally). If you can't make the Wizard work: try another browser
on another OS. Use as vanilla browser configuration as possible: no
extensions, no fancy options.

Notes:

I don't believe browser extensions were the issue (I had them turned
off or not installed in all of the combinations that I tried) but I do
think there might be a subtle interaction between the Wizard and the
default configuration of some browser/OS combinations I used that
MAY be the root cause of my problem

I never did get the bypass URL to work. Why is still an open question,
but because the C7100V's onboard web server returns a custom 404, I think
the problem is on the C7100V.