setting for Firefox and Vivaldi

userChrome.css

#forward-button, #back-button, #context-sendpagetodevice, #context-inspect-a11y, #context-savepage, #context-selectall, #context-viewsource, #context-inspect, #context-screenshot, #context-openlinkintab, #context-openlink, #context-openlinkprivate, #context-bookmarklink, #context-sendlinktodevice, #context-viewpartialsource-selection, #context-sendimage, #context-setDesktopBackground, #unified-extensions-button, #star-button, #PanelUI-menu-button, menuseparator { display: none !important; }

:root {
	--tab-min-height: 25px !important;
        --urlbar-min-height: 20px !important;
}

.browserContainer > findbar {
	position: fixed;
	top: 1;
	left: 0;
	width: 100vw;
	height: 40px;
	z-index: 2147483647; /* Ensure the Findbar is on top */
	background-image: url(footer_re.png) !important;
	background-position: top right !important; /* Set background image to the top right corner */
	background-color: #222127 !important;
}

userContent.css

@-moz-document domain("youtube.com") {
	#background { opacity: 0!important; }
	#search-icon-legacy { background: #0f0f0f!important; }
}

@-moz-document domain("tweetdeck.twitter.com") {
	.js-gryphon-beta-btn { display: none!important; }
}

@-moz-document url(about:newtab), url(about:home) {
	body {
		background-color: transparent !important;
		background-image: url(background.png) !important;
   		background-size: 100% !important;
   		background-size: auto 100% !important;
	}
	.logo-and-wordmark { display: none!important; }
	.search-inner-wrapper { margin-top: 35vh!important; }
}

vivaldi.css

#header {
	height: 33px !important;
	min-height: 33px !important;
}

#tabs-tabbar-container { height: 33px !important; }

#main {
	flex-direction: row-reverse;
        flex-wrap: wrap;
}

.mainbar {
	width: 50%;
	height: 32px;
}

.toolbar-mainbar { height: 32px !important; }

.bookmark-bar {
	width: 50%;
	height: 32px !important;
}

.observer { justify-content: flex-end; }

.inner {
	height: calc(100vh - 65px);
        flex-basis: 100% !important;
}

.vivaldi, .sync-and-trash-container { display: none !important; }

#tabs-container { padding-left: 0 !important; }