They measure lots of client-side feature usage, in part so that they know when they can deprecate something. Here's a list and short explanation [0]. Firefox h

They measure lots of client-side feature usage, in part so that they know when they can deprecate something. Here's a list and short explanation [0]. Firefox has something similar [1] as part of Telemetry, although they measure less things [2]. [0]: https://chromium.googlesource.com/chromium/blink/+/master/Source/core/frame/UseCounter.h#47 https://chromium.googlesource.com/chromium/blink/+/master/So... [1]: http://gecko.readthedocs.io/en/latest/toolkit/components/telemetry/telemetry/collection/use-counters.html http://gecko.readthedocs.io/en/latest/toolkit/components/tel... [2]: https://dxr.mozilla.org/mozilla-beta/source/obj-x86_64-pc-linux-gnu/dom/base/UseCounterList.h https://dxr.mozilla.org/mozilla-beta/source/obj-x86_64-pc-li...