In bug 1639774, we added telemetry probes to detect whenever Picture in Picture is enabled or disabled.

We currently test for scalar changes. However, we are missing tests for telemetry events whenever the pref media.videocontrols.picture-in-picture.video-toggle.enabled is toggled. (Missed this in my review. My bad!)

Having these tests can ensure that we are recording events as expected.
(testing events documentation). We also have existing tests for telemetry that can be used as reference.

Right now there is a severe frequency of failures for the test browser_telemetry_togglePiP.js (see Bug 1755274).
I think we should hold off from modifying the test until we can determine the reason for the sudden spike in failures.