Sorry, I just realised my comment was ambiguous. The apps claim not to support Firefox, and then I'd just close the app without trying with a spoofed UA - so it's not necessarily a technical issue.
The only one I have bookmarked is https://getmibo.com, which claims to "currently only work in Google Chrome"
Honestly, when I see an application that works with Chrome exclusively, I just conclude that the application is either bad or not finished yet and ignore it.
I understand Safari because it's just a massive pain to develop for because you need custom hardware (and because it lags behind in implementing open standards), but Firefox is perfectly fine for any decent JS application, even if its JS engine is a bit slower. User agent filtering is a thing of the past, web developers need to fix their shitty apps instead of forcing Chrome down everyone's throats.
The only one I have bookmarked is https://getmibo.com, which claims to "currently only work in Google Chrome"