Mostly internal stuff, the source is now nicer to read I'd say (also has typescript annotations).
Also the PiP menu item is now at the top of the menu.

Added a menu where you can select the default action for Windowed to take per domain.
That was also in version 27 from a couple of minutes ago, but this version also has a stupid bug fixed

Added a menu where you can select what action you want to take instead of asking every time.

Also added Picture in Picture support, which would be cool if Firefox would expose that to extensions.

I know I spend way too much time on this, but the icon now tries to fit to your theme. Let me know if it doesn't work for you theme, I might need to add old icons back anyway, if not supported by the theme. Also the icons are now generated on runtime, which makes it a lot easier for me to play with them :)