set caret on mount as we usually do, so FF doesn't enter 2 newlines 🤯

src/components/views/elements/MessageEditor.js

@@ -144,12 +144,7 @@ export default class MessageEditor extends React.Component {
 
     componentDidMount() {
         this._updateEditorState();
-        const sel = document.getSelection();
-        const range = document.createRange();
-        range.selectNodeContents(this._editorRef);
-        range.collapse(false);
-        sel.removeAllRanges();
-        sel.addRange(range);
+        setCaretPosition(this._editorRef, this.model, this.model.getPositionAtEnd());
         this._editorRef.focus();
     }
 

src/editor/model.js

@@ -61,6 +61,16 @@ export default class EditorModel {
         return null;
     }
 
+    getPositionAtEnd() {
+        if (this._parts.length) {
+            const index = this._parts.length - 1;
+            const part = this._parts[index];
+            return new DocumentPosition(index, part.text.length);
+        } else {
+            return new DocumentPosition(0, 0);
+        }
+    }
+
     serializeParts() {
         return this._parts.map(({type, text}) => {return {type, text};});
     }