No more cross to close my windows?

Good evening

I no longer have the cross to close my windows in Firefox, but I think it's also the case in IE and Chrome?

1 - What are the solutions (SIMPLE solutions) to recover this red cross?

2 - Firefox takes a long time to launch upon opening? IE and Chrome do too, although I use them less but still.

After scanning, no issues!!!

Thank you for your quick replies!!!

(Not a beginner but not very skilled)

Thank you for all your answers!

Have a good evening!