Odd behavior when clicking on a URL

[BAG]

If I start Firefox by clicking on an icon for Firefox ("C:\Program Files\Mozilla Firefox\firefox.exe"), it opens the Firefox I expect, with bookmarks, other bookmarks, etc.(130.0.1).

If I click on a URL (e.g., https://duckduckgo.com/) it opens what seems to be a minimalist Firefox (see the attached screenshot).

How to go back to the preferred behavior?

[BAG]

I traced it to what sometimes happens when I click on something that I expect would come up in a new tab on the already running Firefox. Most of the time that is indeed what happens. But occasionally doing something like that opens a fresh instance of Firefox (related to the original issue above; ask if you care).

This frequently happened when I used CoffeeCup HTMLeditor; from within it, one can test the html, and doing this frequently birthed a new Firefox.

Why?