[Affected versions]:
Nightly 79.0a1 (2020-06-22)
Beta 78.0b9 (64-bit)
Release 77.0.1

[Affected platforms]:
MacOs 10.14

[Preconditions]
Have devtools.responsive.browserUI.enabled = false

Steps :

1- Launch the Firefox browser
2- Reach youtube
3- Hit Cmd+option+M in order to start Responsive Design Mode, have both "reload when touch simulation is toggled" and "reload when user agent is changed" CHECKED, and Enable Touch Simulation.
3- try opening pip by clicking button
4- disable touch simulation
5- try opening pip by clicking button once again

Expected Results :
pip should work with Touch simulation on and off

Actual Results :
user cannot open pip by clicking.

Thank you for reporting this Clara! It's certainly a bug that should be addressed. It also raises the question of whether or not RDM should be showing PIP on a simulated mobile device. I don't believe we do this on Firefox Android or iOS, so we probably shouldn't be Pip in when simulating a mobile device in RDM.

Working for me, while testing Bug 1647322 which requires PiP to reproduce. Is this problem still occurring for you?

Hi!

I've just tested this in macOs 10.14 and windows 10 pro and that's correct, I cannot reproduce this anymore either.

Best,
Clara

Likely fixed by the landing of Bug 1625925, but I'm not sure so I'm not going to mark this as a duplicate.