Completely my fault. I downloaded a program (via CNet which I normally trust) and the fine print (which I only skimmed) gave them permission to download an Add On called Arcade Giant. I make a habit of going through the lists of whatever “extras” a program is going to download so that I can reject them all. In this case my brain must have been half asleep. It wasn’t a yes or no option. The fine print automatically gave permission. I was able to delete the program very soon after downloading and all seems to be back to normal now. By the way, I do use Firefox and normally have no problems. I wonder if those having similar issues to mine in Firefox also downloaded this Add-On to Firefox and didn’t realize it.
This seems to be a ‘feature’ of the latest version if the Firefox browser. You are probably seeing pop-up ads also. I do not believe these benefit the web page, but do benefit Mozilla Corporation. I switched browsers a while ago, and downloaded Google Chrome. No more underlines, and much fewer pop-up ads (none on BTT).