I didn't know about any of the politics behind the scenes until I started reading this comment section. I'm one of said lefties who generally cares about politics and will switch products to a more ethical alternative, however in FF's case, I didn't know anything.
I only switched, because the UI sucks!
It lacks features, especially when it comes to bookmarks, tabs, and sessions (or lack thereof).
I tried to stick by it, I downloaded extensions, but then Vivaldi came along and they got the design right. So, I switched!
I'm inclined to think that folks are switching, because these days you need a browser to be much more than a window to surf the web. A browser is more or less an OS inside an OS. I do most of my work inside a browser window. We need features that help us organize, streamline work, and make us productive. FF couldn't even get the bookmarking feature right, which is why there were an infinite number of extensions. I don't know what they were waiting for. Using FF was getting too frustrating. There's an art to designing user interfaces. They would do well to learn from Vivaldi.