That's strange if it just happened suddenly. Here are a couple things to check:

(1) Dark Reader extension

Thank you for sharing your add-ons list. This extension will flip pages to a dark theme. If you didn't install it yourself, do you share your computer with someone else? See: Disable or remove Add-ons.

(2) High Contrast

If you use a High Contrast theme on Windows, set Firefox to ignore that: Disable high contrast mode in Firefox

(3) Browser theme

For some pages, Firefox will try to match your browser theme. If you are using the Dark or System theme, try the Light theme instead: Use themes to change the look of Firefox.

(4) System theme override

Firefox can inform sites of your light/dark preference based on your system theme. You can override that if necessary. Since the details are a bit arcane, I'll add info on that if you need it.

Note that your System Details list shows that you have the Dark Reader extension installed.

• {name: Dark Reader, type: extension, version: 4.9.39, isActive: TRUE, id: addon@darkreader.org}