`userChrome.css` to fix PWA on Firefox

userChrome.css

:root {
    /* Reduce the height of the title bar on GNOME */
    --tab-min-height: 24px !important;
}

#star-button-box,
#star-button {
    /* Hide the bookmark button */
    display: none !important;
}

#nav-bar {
    /*margin-top: -40px !important;
    opacity: 0 !important;
    pointer-events: none !important;*/

    /* Hide the address bar (the textbox for URLs) */
    visibility: collapse !important;

    /*display: none !important;*/

    --random-variable-to-prevent-syntax-error-for-empty-block: 0px;
}

#PersonalToolbar {
    /* Hide the address bar (the textbox for URLs) */
    visibility: collapse !important;
}

/* Make the Tab Bar container act as a static Title Bar */
#TabsToolbar {
    background-color: transparent !important;
    --tab-min-height: 28px !important; /* Compact GNOME height */
}

/*#TabsToolbar .toolbarbutton-1,*/

#tabs-newtab-button,
.tabs-newtab-button {
    /* Hide the new tab button */
    display: none !important;
}

/* Hide all tab-specific UI elements */
.tab-close-button,
.tab-icon-image,
.tab-throbber,
#tabs-newtab-button,
#alltabs-button {
    display: none !important;
}

/* Force the container to let the tab expand */
#tabbrowser-arrowscrollbox {
    display: flex !important;
}

/* Erase the background highlighting the active tab */
vbox.tab-background {
    display: none !important;
}

/* Style the ACTIVE tab to look like a title */
.tabbrowser-tab[selected] {
    position: absolute !important;
    left: 50% !important;
    transform: translateX(-50%) !important;
    background: transparent !important;
    border: none !important;
    box-shadow: none !important;
    pointer-events: none !important; /* Makes it non-draggable/clickable */

    /* Remove tab-like appearance */
    background: transparent !important;
    border: none !important;
    box-shadow: none !important;
    margin: 0 !important;
    padding: 0 !important;
}

/* Hide background tabs entirely so they don't overlap */
.tabbrowser-tab:not([selected]) {
    display: none !important;
}

/* Center the text in the tab and format it */
/*.tab-content {
    justify-content: center !important;
    background: transparent !important;
}*/

.tab-label {
    font-weight: bold !important;
    font-size: 13px !important;
    color: currentColor !important;
}

/*.tabbrowser-tab,
.tabs-newtab-button,
#alltabs-button,
.tab-drop-indicator {
    display: none !important;
}*/

#TabsToolbar {
    background: transparent !important;
    margin-bottom: 0 !important;
}

#titlebar {
    visibility: visible !important;
}

.titlebar-buttonbox-container {
    visibility: visible !important;
    display: flex !important;
}

#PanelUI-button {
    visibility: visible !important;
    position: fixed !important;
    top: 0px; /* Adjust to align vertically with window buttons */
    right: 110px; /* Moves it to the left of the 3 window buttons */
    z-index: 999 !important;
    display: flex !important;
}

/*#PanelUI-menu-button {
    padding: 2px !important;
}*/

z_LOCATION.md

Path: ~/.local/share/firefoxpwa/profiles/00000000000000000000000000/chrome/userChrome.css