When using the picture-in-picture feature, the spacebar is meant to be a keyboard shortcut to pause or continue the video. This is shown on the tooltips for the UI elements in the picture-in-picture feature, and on the keyboard shortcuts in https://support.mozilla.org/en-US/kb/about-picture-picture-firefox#w_keyboard-shortcuts However, what actually happens when I press the spacebar key is it instead activates the last UI element to have been clicked on in the picture-in-picture. For example, if I have last clicked the fullscreen icon to make the picture-in-picture fullscreen, pressing the spacebar will toggle the fullscreen mode, and not pause or continue the video.