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I believe this is the game you are referring to: https://lichess.org/IPhkCfYB#8 As you can see, it's an Atomic Chess game, and in Atomic Chess when a piece is captured, all adjacent pieces are destroy…

Click on the game. Then click on the hamburger menu in the bottom right. You'll find the Delete button there. https://i.imgur.com/1CplAqC.png

Yep, the FEN has "KQkq" in it, but the king has obviously already moved, so it's interpreted as a Chess960 position, in which O-O-O would indeed be a legal move.

This seems relevant: https://chess.stackexchange.com/questions/2217/crazyhouse-bughouse-openings

No problem, however I have just checked the app and unfortunately there doesn't seem to be a similar option as on the desktop site.

There is a GG button which appears at the end of the game which you can press. It automatically sends the message "Good game" to your opponent.

Though I am not a Firefox user myself, I commend you for the effort you put into this extension. It looks really well-designed and I am sure many Firefox users will find it helpful!

Start by watching all the videos in John Bartholomew's "Chess Fundamentals" series. Here is the first episode: https://www.youtube.com/watch?v=Ao9iOeK_jvU

It is already possible to block players by going to their profile and clicking the Block button in the top right. What do you mean by valorate?

Do lots of tactics puzzles and learn a bit of opening theory. And play long time controls to help you improve.