What OS? What Desktop? X11 or Wayland?

Try downloading Firefox from Mozilla, run firefox-bin from the folder and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Operating System: openSUSE Tumbleweed 20221013 KDE Plasma Version: 5.26.0 KDE Frameworks Version: 5.99.0 Qt Version: 5.15.6 Kernel Version: 6.0.0-1-default (64-bit) Graphics Platform: X11 Processors: 12 × Intel® Core™ i7-9850H CPU @ 2.60GHz Memory: 125.2 GiB of RAM Graphics Processor: Mesa Intel® UHD Graphics 630 Product Name: HP ZBook 17 G6

I am running Ubuntu. I don't know which desktop and I think it is X11.

I downloaded & installed Firefox in a temp directory & then ran firefox-bin, as suggested.

Testing with https://www.wunderground.com/forecast/us/or/molalla shows same problem.

OK, after checking my "Settings" menu, I am running X11. I don't the "Desktop" name, but the menu does say that the OS name is Ubuntu 20.04.5 LTS, 64 bit, Gnome version 3.36.8.

Happening in the distro and Mozilla version of Firefox... sounds like a desktop or OS issue. Try another desktop or get your Google on...

You should have a live usb stick of another OS that you can boot to and test or fire up a VM. Shameless plug... https://download.opensuse.org/distribution/leap/15.4/appliances/iso/openSUSE-Leap-15.4-KDE-Live-x86_64-Media.iso

I reset my "Keyboard Shortcuts" to the original (Dell) manufacturer's state -- No effect; I still get 2-second delayed scrolling.

My only other OS's are Windows 7 & Ubuntu, on a separate machine which does not display the 2-second problem and which can't be connected to the online Ubuntu-only machine which has the problem.

Unless someone has a specific solution, I guess I'll have to tolerate a permanent 2-second delay online.

I don't want to risk reinstalling or updating my online Ubuntu, because I may loose the list of over 90,000 Firefox files which, among several million, are flagged as "saved" in my ongoing picture-collecting project.

Do you have similar setting in Gnome? see screenshot Have you tried setting things back to defaults or changing the keyboard?

I tried some defaults, and they made no difference.

I only have one keyboard for this (Inspiron 3847) computer, but I think I could use a backup: So, I am buying another one from Dell. I'll post the result.

I received my new Dell keyboard today.

Same problem: Scrolls one line after keyboard "Enter" is held down, then waits about 2 seconds before a rapid scroll of multiple lines below it.

New keyboard... I don't think this is a keyboard issue. Can you fire up a VM or live usb stick to see if you have the same issue. https://www.youtube.com/results?search_query=live+usb+stick+linux

With this option you are not installing anything, just booting from another device and OS to test to see if you have the same issue on the hardware giving you problems now. This is a good one J... lets get to work.  ;-)) Why not get another drive (storage is cheap) and do a fresh install on the same problem computer. I say try openSUSE on a live usb stick or new disk.  ;-))

I think your advice is good, but I'm tired of fighting this minor problem of a 2-sec delay.

I'm not going to try anything more -- thanks anyway.