I've been using Firefox since 2002, always loyal because it works as I expect a browser to work. For users like me who see the benefits of Firefox being the only browser worth losing the benefits of native browsers (Safari/Edge), the only real place we'd move to due to sufficient issues is to those native browsers.
The new Chromium-based Edge[0] for someone like me, who would never use Chrome, is the only cross-platform alternative that could pull me away from Firefox. Native power usage advantages on Windows, with portability to other platforms and Chromium's speed advantages makes it a very attractive choice. I hate to see this happen to Firefox, but they don't have a lot of room for error. I've been using "ChrEdge" at work, and it's already a great browser as it is.