Affected versions

• Firefox 74.0b6
• Firefox 75.0a1

Affected platforms

• Ubuntu 18 x64
• Windows 10 x64
• macOS 10.11

Steps to reproduce

1. Play a video from youtube.
2. Use the combination CTRL+SHIFT+] from keyboard.
3. Make sure that PiP is in focus and use the combination from step 2 again.

Expected result

• PiP is closed.

Actual result

• Nothing happens.

Regression range

• If it's a regression, I will try to find it as soon as possible.

Additional Notes:

• If the focus is on youtube, then the shortcut works to close the frame.

Regression range
This doesn't appear to be a regression. Checked with builds from 2019-09-06 that appears to be at the time the feature was implemented.

Additional note: the shortcut "Ctrl+Shift+]" works if the video is focused instead of the Pip window.

To make this work, we should include xul:key elements in the player.xhtml document that are the same as the ones in the main browser window. We will also need a xul:command element that toggles picture in picture via its oncommand attribute, similar to the one in the main browser window.

The handler should probably just close the window - it doesn't really make sense to re-enter picture-in-picture from within the player window.

To elaborate slightly:

Once you've got the <key> and <command> in player.xhtml, I'd have the <command> oncommand attribute call something like Player.onCommand. Then I'd implement onCommand inside of the Player object in player.js.

The onCommand method should then close the window with something like:

PictureInPicture.closePipWindow({ reason: "player-shortcut" });

and that should do it!

https://hg.mozilla.org/mozilla-central/rev/0f8cb57c27ac

Reproduced the initial issue using an old Nightly build 75.0a1 on Windows 10.
Verified - Fixed in latest Nightly 84.0a1 84.0a1 (2020-10-22) and Beta 83.0b3 (build id: 20201022171613) using Windows 10 and Ubuntu 18.04.