I can't login to the work-paid-for version of Microsoft Copilot with Firefox, for some reason. I've had one or two others - I think they were internal CMU website tools. And even more niche: My kids took a ski lesson last year at Snowbird and the website with their report card rejected anything that didn't identify as Chrome. It _worked_ with mobile FF, but it popped up a "YOU SHOULD USE CHROME" banner and wouldn't let me past.
So, small stuff. Maybe Copilot isn't working because of ublock, though.