UserAgent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:62.0) Gecko/20100101 Firefox/62.0

Steps to reproduce the problem:
1. Visit https://mdn.mozillademos.org/en-US/docs/Web/API/Media_Streams_API/Constraints$samples/Example_Constraint_exerciser?revision=1411870 At the top, sampleRate is listed as an available constrainable property.
2. change the "Requested audio constraints:" to {"sampleRate": 8000} then click "Apply Constraints".

What is the expected behavior?
In the "Actual audio settings" box, the sampleRate does not change. In my case, it stays as "sampleRate": 48000, but your computer could show slightly different one like 41000. Nevertheless, setting it to 8000 doesn't work.

What went wrong?
Chrome says it supports the "sampleRate" media constraint (can be obtained via navigator.mediaDevices.getSupportedConstraints() in the console), but it doesn't, as seen in the Mozilla demonstration.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 69.0.3497.81 (Official Build) (64-bit)  Channel: stable
OS Version: 16.04
Flash Version: 31.0.0.108