I often talk to people reporting a broken website in qutebrowser where it turns out to be due to a Firefox user agent.

Some examples (there are lots more via IRC/Reddit/...):

https://github.com/qutebrowser/qutebrowser/issues/4302 https://github.com/qutebrowser/qutebrowser/issues/3822 https://github.com/qutebrowser/qutebrowser/issues/1187