https://pagespeed.web.dev/ Who are you using for DNS? Also, you can add this add-on. https://addons.mozilla.org/en-US/firefox/addon/load-time/

Forgive my ignorance, but that website only appears to show expected performance and not current device performance? I tested for google.co.uk on both Chromium and FF and although FF took an age to show me any results it showed the same scores.

As a non scientific metrics example I did a stop watch test loading the same page in Chromium and FF. I used https://planetrock.com

Chromium - 2.5s FF - 8.75s

google.co.uk - circa 12s in FF

Once FF has loaded a page, it gets faster (cached?) on subsequent loads.

Current DNS config ---8< resolv.conf nameserver 192.168.0.16 << internal (local) DNS nameserver 192.168.0.1 << Netgear router, which directs to cloudflare 1.1.1.1 domain ytc ---8<

Yes, I have flipped 0.1 and 0.16 it makes little difference. :-(

Hardware (desktop) ---8< scpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian Address sizes: 39 bits physical, 48 bits virtual CPU(s): 4 On-line CPU(s) list: 0-3 Thread(s) per core: 1 Core(s) per socket: 4 Socket(s): 1 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 158 Model name: Intel(R) Core(TM) i3-9100 CPU @ 3.60GHz Stepping: 11 CPU MHz: 800.023 CPU max MHz: 4200.0000 CPU min MHz: 800.0000 BogoMIPS: 7200.00 Virtualisation: VT-x L1d cache: 128 KiB L1i cache: 128 KiB L2 cache: 1 MiB L3 cache: 6 MiB ---8<

Okay, I decided to have a further play with DNS and have moved 1.1.1.1 to the top nameserver search.

This makes a world of difference! (Sorry, it just had not occurred to me to override the router selection) So, this points at the netgear router? But why would only FF suffer issues?

I'm going to carry on duel running FF and Chromium and see how things go.

(And yes I know how annoying it is in IT to be told "it's slow", with no metrics to back it up :-) )

So, unsure why pre-pending 1.1.1.1 in my resolv.confs(s) has fixed this, obviously more digging needed.

I've changed all my Mac, Solaris and Linux boxes to ---8< search ytc nameserver 192.168.0.16 <<< internal DNS nameserver 1.1.1.1 nameserver 192.168.0.1 <<<< Netgear router (which also goes to 1.1.1.1) nameserver 127.0.0.53 <<<< only on Linux boxes ---8<

And delays have gone. Now switched back to using FF everywhere :-)

Thanks for the hint, it just had not occurred to me that the netgear router might be the issue. But the question still remains .... why did it only affect FF??????