[onCutOrCopy] Creating the phony copy div at the same level as the real div (#1350)

* Creating the phony copy div at the same level as the real div

* Added COMPAT desc for the Firefox scroll jump fix

* Update after.js

* Update after.js

packages/slate-react/src/plugins/after.js

@@ -233,6 +233,15 @@ function AfterPlugin() {
     div.setAttribute('contenteditable', true)
     div.style.position = 'absolute'
     div.style.left = '-9999px'
+
+    // COMPAT: In Firefox, the viewport jumps to find the phony div, so it
+    // should be created at the current scroll offset with `style.top`.
+    // The box model attributes which can interact with 'top' are also reset.
+    div.style.border = '0px'
+    div.style.padding = '0px'
+    div.style.margin = '0px'
+    div.style.top = `${window.pageYOffset || window.document.documentElement.scrollTop}px`
+
     div.appendChild(contents)
     body.appendChild(div)