I just had a mini panic attack when I opened up the newly downloaded @firefox Dev Edition and found that the UI was entirely flipped because Mozilla decided that just because I'm in Lebanon I’ll want my UI & Lang preferences to be RTL. @mozilla assumed wrong. Instant uninstall.

It's really easy to change that setting. I've had many programs use my native language, but always want english. I appreciate the effort they make though, especially for those still with bad english skills, like my parents for example.

It’s not easy to change the settings. I literally have to search for where to do it and even then it always switches back for some reason. Also you'd think that they're good enough to provide lang settings based on your years of previous usage.

Distribution of Firefox localizations on desktop platforms is primarily a download-time thing. A given download contains only one language. There's some support for installing more and switching between them, but it's not designed to be the primary path for users.

The browser sends a lang header. With a list of preferred languages in desired order. Just use that instead of messing up with geoip. And it's not me saying that. It's a recommended practice.