Most likely a scam. Definitely not from Mozilla (the maker of Firefox).

Tnx. It appeared as a new tab, just after I updated Mozilla Firefox. Do you think I need to take any action to prevent this from occuring again? This is on my iMac OS Catalina. Is it a setting in FireFox Preferences?

Hmm, check your Add-ons?

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Command+Shift+a (Windows: Ctrl+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Any improvement?

Tnx. Only DuckDukGo is above "Recommended Extensions and below Enabled. I downloaded AVG for Mac and am waiting while it scans. Tnx for mentioning Extensions.