Modern browsers are platforms for modern apps and especially for communication apps, because the Internet is primarily about communications and browsers haven't been about rendering content for a long time now.
Consider: Slack, Gitter, Facebook Messenger, Gmail, Hangouts, Google Inbox, Fastmail, web.whatsapp.com and web.skype.com.
You can make an argument that Firefox should stay neutral. But I don't believe that many use Chromium instead of Chrome. For one because you can't find decent builds, unless you're on Linux, but also because people that don't want Chrome because of Google's services probably use Firefox, because Chromium is still integrated with Google (Web Store, Sync), while providing a poor experience (no PDF viewer, no Flash, no DRM, or any other proprietary bits).
Good thing that PDF.js, the PDF viewer from Firefox, ended up on Chrome's Web Store, so you can add it to Chromium. Which is the main difference between Mozilla and its competition: when Mozilla improves Firefox, it tends to benefit everybody.
