Space (Complete) per Stanik123

To completely change your browser (theme + new panel background), you must:

1) Search "about: profiles" in your browser
2) "Open folder" at "root directory"
3) Create a folder named "chrome" here
4) Save this picture into it: "https://ctrlv.cz/shots/2019/05/04/qZCn.png"
5) Create the file "userContent.txt" and copy:
@-moz-document url("about:newtab") {

body {

background-image: url('qZCn.png') !important;
background-position: center center

}

}

5) Rename the file to "userContent.css"
6) Restart FireFox and enjoy the new look ...