As mentioned in other threads, great script!

I cannot rate it unless I create a new thread so ... well ... here I am.
Love it!

Thanks @mikedl

It's originally from this thread
http://forum.userstyles.org/discussion/31373/fade-in-effect-on-web-pages/p1
You had cameo appearance there

You can modify the script and change it, for example, like this

GM_addStyle("@keyframes slideInRight {\
from {\
transform: translateX(2000px);\
}\
to {\
transform: translateX(0);\
}\
}\
@keyframes slideOutLeft {\
from {\
transform: translateX(0);\
}\
to {\
transform: translateX(-2000px);\
}\
}\
html {\
animation-name: slideInRight;\
animation-duration: 1s;\
}\
.kthxbye {\
animation-name: slideOutLeft;\
animation-fill-mode: forwards;\
}")
addEventListener("beforeunload", function() {
document.documentElement.classList.add("kthxbye");
})

More cool CSS animations
http://daneden.github.io/animate.css/

LouCypher, LOL! That's way too cool! Nice!