The good thing is that the source code is mostly* out there and you or someone else can figure out what it's doing.
[*] don't know about drm stuff
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Each Firefox download has a unique identifier (2022): https://news.ycombinator.com/item?id=30715163
Eye-opening and pretty straightforward with e.g. mitmproxy. Strip TLS with a temporarily trusted self-signed cert to get the whole picture.