Disabling telemetry is one of the first things that nearly all advanced users do when using Firefox, or when using other products known to include telemetry that can be disabled.

So now any telemetry data that are collected are distorted, given that some of the wisest and most valuable users just aren't included at all because they've disabled telemetry.

Analysis done on the distorted data comes to distorted conclusions.

Product decisions made based on such distorted conclusions end up distorting the usability of the software.

Firefox has collected telemetry for quite a while now, yet I've yet to see that translate into any identifiable improvement.

Worse, a lot of very common Firefox user requests like "make it faster" and "make it use less memory" seem to get minimal attention.

I think Firefox would be a better product, and thus a more widely used product, if the telemetry were to be completely ditched, and the common user complaints that are voiced again and again in all sorts of discussion venues were listened to instead.