Version 62 of Firefox will integrate a new add-on called Firefox Monitor that basically informs users if their email accounts have been compromised. The add-on uses the popular Have I Been Pwned database backend to check if the account has been compromised in data breaches.
https://www.notebookcheck.net/Firefox-62-comes-with-Firefox-Monitor-that-notifies-if-you-ve-been-pwned.324598.0.html
Only EN-US? The world is bigger than that.
All good stuff online comes in English first. However, in this case, I don't think it's such a big thing. Just another memory/CPU hog that keeps checking for changes on a website that you could check manually for yourself, really.
Firefox reminds me of what browsers like Opera started to do in order to get attention. Throw everything but the kitchen sink into their browser to make it the Swiss army knife of browsers. Mozilla seems really focused on privacy as if they think this is their niche in browsers. Although I feel most people really don't care about privacy and in fact accept that the internet is just not a place to consider private. Chrome being so popular obviously means those users are not too concerned about privacy and so probably are not considering Firefox. I do think Firefox is facing the same issues as Microsft's Edge browser. A decent browser that waited too long to compete with Chrome and has become irrelevant.