It's helpful for Mozilla's engineers to be able to measure how Firefox for Android behaves in the real world. The Telemetry feature provides this capability by sending them performance and usage information. As you use Firefox, Telemetry measures and collects non-personal information, such as memory consumption, responsiveness timing and feature usage. It then sends this information to Mozilla on a daily basis and we use it to make Firefox better for you.
Firefox also has a Crash Reporter feature that warns you when Firefox closes unexpectedly, and allows you to send this information so the engineers can make Firefox more stable and secure.
You can turn this feature on or off at any time in your Settings: