If you type or paste about:config in the address bar and press Enter, is the page readable, or is that also black on black? If it's readable:

Type or paste color in the search box and pause while Firefox filters the list

Look for browser.display.background_color and try to reset it to default: right-click or Ctrl+click that preference > Reset

Does that work?

Thanks for the idea. Sadly, the about:config screen is also all black.

Okay, what I suggest is the following (details below):

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter/Return

In the first table on the page, click the "Show in Finder" button -- which hopefully you can read amidst the inky blackness. This should launch a new window listing various files and folders in Finder.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit (or is it Firefox > Quit on Mac??)

Pause while Firefox finishes its cleanup, then rename prefs.js to something like prefs.old.

Start Firefox back up again. Settings should mostly return to defaults, including colors.

If you lost too much in that process, it's possible to manually edit the prefs.js file instead of starting a fresh one, but the details are beyond the scope of this reply.

Genius! I was able to see a few of the buttons and thankfully "Show in Finder" was one of them.

It's back to its original self! It kept all my bookmarks, extensions, history, etc.

This is the first time I've ever posted to a user support forum and didn't really expect to hear from someone, especially so quickly.  ; )

Thank you so much! I truly appreciate your time and expertise!

NC_P

Thank you for the update. If you notice anything important missing, like settings for an add-on, you can open that prefs.old file in a text editor and probably find it in there. We'll be here if you need any help along those lines.