The addon adds content to the editor itself, e.g. Wordpress
The following content is added:
"div id="simple-translate" class="simple-translate-light-theme"
div
div class="simpie-translate-button isShow" style="background-image: url('moz-extension ://7bd028b3-62a8-43e5-918c-13744618dc89/icons/512.png'); height: 22px; width: 22px; top: 3648px; left: 38px;"/div
div class="simple-translate-panel " style="width: 300px; height: 200px; top: 0px; left: 0px; font-size: 13px;"
div class="simple-translate-result-wrapper" style="overflow: hidden;"
div class="simple-translate-move" draggable="true"X/div
div class="simple-translate-result-contents">
p class="simple-translate-result" dir="auto"X/p
p class="simple-translate-candidate" dir="auto"X/p
/div
/div
/div
/div
/div"

Better than official google extension on chrome.
Upd: is currently broken

good add

Very good!

Very convenient add-on. Simple, with various settings.

Bravo!

! Merci !

4 stars because it doesn't show which source language it translates from. It is important to many of us to know the source language. I hope the developer fixes this as it will make it the best translation extension.