Is your feature request related to a problem?
https://github.com/black7375/Firefox-UI-Fix/blob/master/src/padding/_first_tab.scss#L6-#L9
This current code doesn't work when having pinned tabs and the tabbar overflow is visible

The solution I'd like

:root:not([sizemode="normal"]) .titlebar-spacer[type="pre-tabs"] {
  display: -moz-box !important;
  width: var(--space-left-tabbar) !important;
}

However this code works always.

Screenshots or video

Alternatives I've considered

Additional context