Eu sei que esta pergunta é em relação ao FireFox, mas você também pode obter esse recurso no Chrome (o Firefox não permitirá que você insira JS como marcador):
Adicione este código javascript como um URL de marcador:
javascript:void function(b,p)%7Bfunction l(k,c,b,e,g,d,f)%7Breturn"<div style%3D%27position:absolute%3B-webkit-transform-origin: 0 0 0%3B"%2B("background:"%2Bf%2B"%3B")%2B("width:"%2Be%2B"px%3B height:"%2Bg%2B"px%3B")%2B("-webkit-transform:"%2B("translate3d("%2Bk%2B"px,"%2Bc%2B"px,"%2Bb%2B"px)")%2B("rotateX(270deg) rotateY("%2Bd%2B"deg)")%2B"%3B")%2B"%27></div>"%7Dfunction o(k,c,d,f)%7Bfor(var j%3Dk.childNodes,n%3Dj.length,m%3D0%3Bm<n%3Bm%2B%2B)%7Bvar a%3Dj%5Bm%5D%3Bif(1%3D%3D%3Da.nodeType)%7Ba.style.overflow%3D"visible"%3Ba.style.WebkitTransformStyle%3D"preserve-3d"%3Ba.style.WebkitTransform%3D"translateZ("%2B(b%2B(n-m)*q).toFixed(3)%2B"px)"%3Bvar h%3Dd,i%3Df%3Ba.offsetParent%3D%3D%3Dk%26%26(h%2B%3Dk.offsetLeft,i%2B%3Dk.offsetTop)%3Bo(a,c%2B1,h,i)%3Be%2B%3Dl(h%2Ba.offsetLeft,i%2Ba.offsetTop,(c%2B1)*b,a.offsetWidth,b,0,g%5Bc%25(g.length-1)%5D)%3Be%2B%3Dl(h%2Ba.offsetLeft%2Ba.offsetWidth,i%2Ba.offsetTop,(c%2B1)*b,a.offsetHeight,b,270,g%5Bc%25(g.length-1)%5D)%3Be%2B%3Dl(h%2Ba.offsetLeft,i%2Ba.offsetTop%2Ba.offsetHeight,(c%2B1)*b,a.offsetWidth,b,0,g%5Bc%25(g.length-1)%5D)%3Be%2B%3Dl(h%2Ba.offsetLeft,i%2Ba.offsetTop,(c%2B1)*b,a.offsetHeight,b,270,g%5Bc%25(g.length-1)%5D)%7D%7D%7Dvar g%3D"%23C33,%23ea4c88,%23663399,%230066cc,%23669900,%23ffcc33,%23ff9900,%23996633".split(","),q%3D0.001,e%3D"",d%3Ddocument.body%3Bd.style.overflow%3D"visible"%3Bd.style.WebkitTransformStyle%3D"preserve-3d"%3Bd.style.WebkitPerspective%3Dp%3Bvar r%3D(window.innerWidth/2).toFixed(2),s%3D(window.innerHeight/2).toFixed(2)%3Bd.style.WebkitPerspectiveOrigin%3Dd.style.WebkitTransformOrigin%3Dr%2B"px "%2Bs%2B"px"%3Bo(d,0,0,0)%3Bvar f%3Ddocument.createElement("DIV")%3Bf.style.display%3D"none"%3Bf.style.position%3D"absolute"%3Bf.style.top%3D0%3Bf.innerHTML%3De%3Bd.appendChild(f)%3Bvar j%3D"NO_FACES"%3Bdocument.addEventListener("mousemove",function(b)%7Bif("DISABLED"!%3D%3Dj)%7Bvar c%3Db.screenX/screen.width,b%3D(360*(1-b.screenY/screen.height)-180).toFixed(2),c%3D(360*c-180).toFixed(2)%3Bd.style.WebkitTransform%3D"rotateX("%2Bb%2B"deg) rotateY("%2Bc%2B"deg)"%7D%7D,!0)%3Bdocument.addEventListener("mouseup",function()%7Bswitch(j)%7Bcase "NO_FACES":j%3D"FACES"%3Bf.style.display%3D""%3Bbreak%3Bcase "FACES":j%3D"NO_FACES",f.style.display%3D"none"%7D%7D,!0)%7D(25,5E3)%3B
Depois de adicionado, clique no marcador em qualquer site. Você pode clicar para mostrar contornos e arrastar para visualizar como no Firefox.