Opera set the default browser to itself without asking when I installed it. Questionable of course, but it also caused this unusual error that has 0 results on your favorite search engine. There is some level of unintended behavior going on.
Text of the error notification from Windows: "An app caused a problem with your default browser setting, so it was reset to Opera Internet Browser."
Screenshot of all 3 notifications:
Perhaps unusual about my setup: I had manually added a command-line switch to pass to Firefox in these app handlers. (It also makes this a pain to go back to my previous settings!)
What did Opera do to cause this? And what can I do to narrow it down?