So I got around to unpacking it today.
Very interesting, so you sent an Archer C20, a router with 10/100Mbps or "Fast" ports. So I won't even be able to actually hit the full line speed due to packet overheads on Ethernet. Is this a joke?
Anyways, I'll plug it in for a day, run some speedtests, iperf and a tracert, even though we both know it's not my router at fault for international speeds.
Still having the same international issues on ff as well. My steam downloads max out at 11mbps.
Currently have the CI blockbox running tests. Hopefully we can finally convince FF there is an issue.
https://mybroadband.co.za/forum/threads/cool-ideas-fibre-isp-feedback.793061/post-23352092
Above is a post on your MyBB thread, another user in the same area with issues on FF.

Local is now 93.88/93.19, so slightly slower than previous local, this is due to the overheads of 100Mbps ethernet, since Fast Ethernet maxes at 95Mbps about.
International London (which if I remember correctly you have a direct link to):
This is pretty high? Maybe fixed?
upload bad though, forgot to write this in the ticket, which is why I redid all the tests
Vienna:

69/16.
Speed.Hetzner.de files still hover at 3-4MB/s with bursts to 6MB/s rarely.
Overall nothing changed with the new router.
WinMTR has no loss, same as on my original router.
But now here's the interesting thing, I then redid this test, a couple of minutes later, after 1pm:

London is now 36/41Mbps. Above is on the London - Vox, so I realized I did the full speed one on Coreix previously, so tested that to make sure it wasn't that:

Mhm, 32/64Mbps, interesting.
So if I've established my PPPoE connection for under about 10 minutes, I get full speed, after that international drops down.
So testing this theory by rebooting my router, nope still the same speed.
And if you're trying to say it's something on the network that triggered, I disabled WiFi on that router, and only this PC is connected with me keeping an eye on the network tab in the performance monitor.
International might slump, but local CT is still fine:
And "for fun": Johannesburg:
There is something wrong with your international configuration.