From my limited experience of Firefox-as-a-project, coming from the side of Thunderbird:
* Firefox is effectively not a community project. It seems to be ruled with an iron fist by the commercial side of the operation.
* Firefox broke its extensibility - which was the whole rationale of the Mozilla project to begin with.
* Lots of telemetry and call-home mechanisms, so much so that it is difficult to opt out even if you want to - in Thunderbird, and I believe also in Firefox; see : https://superuser.com/q/1672309/122798 (but correct me if I'm wrong and it's an app-specific thing).
* Firefox is effectively not a community project. It seems to be ruled with an iron fist by the commercial side of the operation.
* Firefox broke its extensibility - which was the whole rationale of the Mozilla project to begin with.
* Lots of telemetry and call-home mechanisms, so much so that it is difficult to opt out even if you want to - in Thunderbird, and I believe also in Firefox; see : https://superuser.com/q/1672309/122798 (but correct me if I'm wrong and it's an app-specific thing).