Not often, but it does happen enough times that I have Chrome installed as a backup in case something doesn't work. It's usually the in-house websites (for instance, the ones made for tracking timesheets) that break on Firefox. Not all of them break, of course, but if you're required to submit a form via a particular in-house website and it doesn't load on Firefox, then you're kind of forced to have a backup browser at minimum.

It doesn't happen often enough that I would say that using Firefox is problematic, but if you combine that with people's inherent aversion to change, you can start to see why people are so resistant to even trying Firefox. Unfortunately, it ends up being a self-fulfilling prophecy, since the less people use Firefox, the less the web development teams at these companies would be incentivized to make sure their website works on Firefox