There is a website I visit that takes a long time before it gives me control so I can use my mouse.
I think I may have caught a clue as to what might be going on. I caught a glimpse of a message that said something about long running scripts. Could that be the problem and if so is there anything I can do about it? I have already added it to the compatibility view setting list but that didn't help.

What website is this?

Maybe try a different web browser, or try blocking scripts on that website and see if it still functions.

Some websites have 20 or more trackers running scripts -- nothing to do with the website itself, but taking up your memory and processing power.

Have you tried the uBlock Origin addon? It does a pretty good job filtering out the extra tracking junk.

When you say "or try blocking scripts on that website and see if it still functions." is that what you mean by trying uBlock Origin? Or are there other ways?

uBlock Origin will block most unnecessary scripts, like trackers.
So that's what I'd recommend first.

You can also use the NoScript addon, but that blocks almost everything until you train it. It's useful if you want to see every script a website is loading though.

Most web browsers have some way of blocking scripts built in, but that also blocks all scripts -- and many modern websites don't work without scripts.

I noticed that in Internet Options, "Disable Script Debugging (Internet Explorer)" is checked. Is that correct?

Long running scripts are the bane of Internet Excplorer - it's one of the reasons I never use it. But on my old Surface RT tablet, I am chained to IE and it makes me insane. I stopped it by changing the time the scripts are allowed to run before you get the message, but I'd much prefer they didn't run at all. I have been thinking I will try the NoScript addon and this prompts me to do it.

Yes, Geo, that Disable Script Debugging should be checked.

I've been using Adblock Plus with Firefox since it was first touted on this forum. Is this uBlock Origin addon supposed to be better?

uBlock Origin blocks more by default.
Adblock Plus decided to allow some ads, though you're supposed to be able to turn this "feature" off.
https://adblockplus.org/acceptable-ads