Close Tab on the left ist broken

[tetam01]

When changing the userChrome.css to show the Tab close button on the left it does not work.
But after adding following code to WhiteSur/left-tab-close-button.css it works.

tabbrowser-tab .tab-close-button {
-moz-box-ordinal-group: 0 !important;
order: -1 !important;
margin-inline-start: 0 !important;
margin-inline-end: 8px !important;
}