firefox context menu and tab context menu css for linux http://imgur.com/fv4L3Cwl.png

userChrome.css

menupopup {
	--panel-background: var(--arrowpanel-background) !important;
	--panel-color: var(--arrowpanel-color) !important;
	--panel-border-color: var(--arrowpanel-border-color) !important;
	--panel-border-radius: var(--arrowpanel-border-radius) !important;
	--panel-padding: var(--arrowpanel-padding) !important;
}

menuseparator {
    appearance: inherit !important;
    min-height: 0 !important;
    border-top: 1px solid var(--panel-separator-color) !important;
    border-bottom: none !important;
    margin: var(--panel-separator-margin) !important;
    padding: 0 !important;
}

menuitem:not([type="checkbox"], [type="radio"]), menu:not([type="checkbox"], [type="radio"]) {
    appearance: inherit !important;
    margin: var(--arrowpanel-menuitem-margin) !important;
    margin-left: 0px !important;
    margin-right: 0px !important;
    min-height: 24px !important;
    padding: var(--arrowpanel-menuitem-padding) !important;
    -moz-box-align: center !important;
    -moz-box-pack: center !important;
    background-color: inherit !important;
}

.menu-right {
    width:  12px !important;
    height: 12px !important;
    content: url(chrome://global/skin/icons/arrow-right-12.svg);
    fill: currentColor !important;
    fill-opacity: 0 !important;
    -moz-context-properties: fill, fill-opacity;
}

menuitem:hover, menu:hover {
    border-radius: var(--arrowpanel-menuitem-border-radius) !important;
    background-color: var(--button-hover-bgcolor) !important;
}

.menu-text {
    margin-inline-start: 0px !important;
}