Thats exactly what firefox telemetry data is. It collects things like % of requests over HTTPS, % over IPv6, etc and sends anonymized stats to Mozilla.
But at the end of the day, I'm just taking someone's word for it that this is all they send, and assumes that it won't change over time in a browser that regularly updates itself.
It'd be a lot more acceptable if there was an option to show me "This is the exact telemetry payload we want to send to Mozilla." And even then you are taking someone's word for it that there isn't some other piece of data hidden in a hash or something, or that the browser isn't secretly sending data.
I'm not quite paranoid enough to do the full monitoring of all network traffic, but how do I reasonably know what is going on without listening to traffic/watching memory at all times? In the end, I'm trusting a faceless corporation that is attempting to put on a facade of trustworthiness.
The only trustworthy computer is an unnetworked one.
> But at the end of the day, I'm just taking someone's word for it that this is all they send, and assumes that it won't change over time in a browser that regularly updates itself.
Actually you aren't. It's quite easy to build your own Firefox and use that, or use say Ubuntu's build if you trust them more. You wouldn't want to audit the Firefox source code yourself, but if Mozilla was intentionally sneaking backdoors into the source code, someone could (and probably would) eventually find that out and you'd be able to verify it by examining your source archives... which means Mozilla would have to be stupid/crazy to try that.
Firefox is open source, and even the telemetry server code is on github, so if you wanted to really dig in you could.
At the end of the day if you want Firefox to make rational decisions about what feature to implement they need to collect some data. That fact alone can't be a problem for anyone who wants to have firefox be a competitive browser.
You don't know there isn't a government official placing a secret camera across the street from you, watching your computer screen through the window, neither.
Eventually, you have to just get on with your life and trust people.
I'm not particularly bothered by the idea that Firefox can see how often private browsing is used. If you don't know what features people use, you can't prioritize development resources. Mozilla doesn't know who is using private browsing, or what they are looking at.
I can certainly respect that it bothers you—but may I ask what browser you intend to switch to? I'm skeptical that you'll find a better, usable option. That's a sad state of affairs for sure, but also the way of things right now.
If Mozilla knows that, then Private Browsing Mode isn't as private as it could be.