That seems like a reasonable compromise to me. I'm happy to send logs if my browser crashes whenever I visit a certain page, and if I know I'm gonna be monitored for that period, I'll isolate my browsing habit to only visit that page. I do not consent, however, to sending everything--even anonymized--on the offchance that Mozilla will see the crash events and use it to flag that domain and maybe fix the issue on that particular page.
That sounds way more reasonable to me.
To my amateur ear, that actually sounds like a good compromise to lessen the blow somewhat more. You should suggest it to Mozilla :)
And if I opt-in to data collection, why would it matter to me whether the stats I'm sending are a result of me being selected as part of a random sample or not? Might as well just _always_ send those stats; it doesn't matter to me.
FTA:
What we plan to do now is run an opt-out SHIELD study [6] to validate our implementation of RAPPOR. This study will collect the value for users’ home page (eTLD+1) for a randomly selected group of our release population We are hoping to launch this in mid-September."
Notably:
"this study will collect ... for a randomly selected group"
[6] - https://wiki.mozilla.org/Firefox/Shield/Shield_Studies
If that's what you're aiming at. Collect the data but keep it local. Install some sort of responsiveness/"problem" monitoring. Ask the user to send data relevant to the problem if a problem occurs. IMHO there is no need to systematically collect user data for that.
Or get the data from a random sample of users. You don't need data from everyone.