Used to work great; in Firefox 132 it often doesn't work when the browser starts and backgrounds all revert to white. Worked great in at least Firefox 109 and earlier. It also no longer affects top menu bar menu backgrounds and right-click menu backgrounds. This is one of the reasons I don't normally update the browser... because it breaks extensions and it's a nightmare and takes hours of time to try to troubleshoot, often with no resolution. Very frustrating.