Hiding single tabs in userchrome.css in Firefox version 103.0

Up until Firefox version 103.0, the following worked in my userchrome.css file:

/* Set --tab-min-height to 0px so tab bar can disappear */
#tabbrowser-tabs {
–tab-min-height: 0px;

/* Restore minimum height when more than one tab */
#tabbrowser-tabs tab {
min-height: var(–hidetabs-tab-min-height);

/* Collapse tab bar when there is only one tab (tab is both first & last) */
#tabbrowser-tabs tab[first-visible-tab=“true”][last-visible-tab=“true”] {
visibility: collapse;

/* Hide the New Tab button when there is only one tab (first visible tab is
adjacent to new tab button) */
#tabbrowser-tabs tab[first-visible-tab=“true”] + #tabs-newtab-button {
visibility: collapse;

The purpose of it is to hide a tab if it’s the only one in the window. For some reason, it stopped working in Firefox version 103.0. Can anyone tell me why?