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.

I've been daily driving Firefox for several years. Everything I use on a daily basis works fine on FF, but every now and then you come across some random site that doesn't load or loads poorly.

The Teams web app doesn't work (I refuse to install the OS level app)

Expedia doesn't render properly in Firefox - some of the sections are missing, but it's not immediately obvious what is missing. It took me a while to figure out why my wife kept having problems with that site, and I had to move her to Chrome to allow her to use it.

I continue to use Firefox because I know when to suspect a website problem might be the browser, but she doesn't have the ability to analyze a situation like this. I have this conundrum with other family members that I support. I want them to use Firefox, but I hate to have them run into an issue because of the browser I recommended.

Bizzarely, Microsoft Word on web seems to be the only thing I've encountered which has FireFox problems, specifically it'll periodically "save" the document I'm typing and then delete the last sentence or two that I changed while it was saving. I think it's some kind of broken state management on the MS side (leave it to MS). That's the only site I've used though, and I've been a daily driver of FF for 10 years.

Sticky desktop notifications don’t work on macOS on FF, which means event notifications from calendar apps disappear within a few seconds, leaving no time to snooze them or act on them in any other way. Queue missed meetings.

Amazon properties (the storefront, Prime) have been quite flaky for a long time now, but that may just be me.

Certainly no major site.

I can't get ticketmaster to work reliably on Firefox. I guess it thinks I'm a bot. I can use Chrome on the same computer and book tickets just fine.

One crap product forcing me to use another crap product! ;)