Actually, that code above doesn’t take into account Firefox container tabs.
Some of the comments on Hacker News explain how to show the container colors:
/* Make the tabs not blend into the background */
.tabbrowser-tab:not([selected]) .tab-content {
background: #58506040;
border-radius: 4px 4px 4px 4px !important;
margin-bottom: 4px !important;
margin-top: 4px !important;
}
Setting transparency on the background element doesn’t cover up the container color.
There are also some rules to revert the changes using CSS here:
https://twitter.com/Mailia/status/1399776195345006593
and here: