YWY Mozilla has stealth released some questionable things through Firefox updates. They've also integrated in Widevine CDM and EME, abandoned XUL in favor of Google's WebExtensions, and removed an extension recently that promoted freedom of speech.
Pretty much, it seems like they want to be Google and have been slowly turning Firefox into Chrome. It's still completely open-source, though. It's just that it will download non-open-source plugins by default. That can be disabled, though.
That said, the browser is still worthwhile. It still has the about:config page that lets you control every aspect of what features it has left. With the right tweaking, it becomes a privacy and open-source focused browser again. Unfortunately, with the direction they've been going, I wonder how long that will last.
If you want a completely FOSS Gecko browser, check out FSF's IceCat or Hyperbola's IceWeasal (not the Debian one). If you just want an open-source one that lets your control everything that matters without dealing with most of Mozilla's nonsense, check out Waterfox or Pale Moon.
