Telemetry went live in Firefox Nightly builds over the weekend. Everyone who wants to contribute to making Firefox better now has an easy new way: opt-in to telemetry.
There are two ways to opt in:
A) Click yes when prompted to report performance
B) Enable it by going to Options/Preferences, then Advanced/General tab
You can check on the data collected by installing my about:telemetry extension.

I often use craptastic internet connections, so I’m hesitant to enable this. Is telemetry likely to send data often enough, or in large enough quantities, to affect regular usage over (say) tethering to a phone using 1x instead of 3G?
I hope the ‘Learn more’ link sends the user to a more informative page in release builds than the Privacy Policy page.
@starwed filed https://bugzilla.mozilla.org/show_bug.cgi?id=667981 for this. Will need to add some more capabilities to our networking api for this
@Archaeopteryx working on it. Easy to read English isn’t my strong side