Netgear R7800: "please upgrade to a version 4 or higher..."

[peter_b]

[PROBLEM]
On a freshly bought, "Netgear Nighthawk X4S AC2600 R7800", I was surprised to get the following message in a Firefox 81.0 on Xubuntu 18.04:

Please upgrade to a version 4 or higher browser so that you can use this setup tool (and see lots of great sites on the Internet!)

...considering that v82.0 is the most recent version of Firefox up-to-date
I also find it interesting that the above quote cannot be found as search string on the Internet (duckduckgo and Google)

[SOLUTION]
Javascript was disabled.
When using the NoScript extension in Firefox, simply allow scripts for "192.168.1.1" (=default LAN IP of the router).

The configuration page seems to work in Chromium (v85.0.4183.83 Official Build), too btw.