Update IS_FIREFOX_LEGACY flag to prevent FF crash (#4237)

* Update IS_FIREFOX_LEGACY flag to prevent FF crash

#4118 and #4150 introduced IS_FIREFOX_LEGACY, but this block of code was not updated to reflect that. This breaks insertion of emoji and unicode characters in slate-react. This change fixes #3855.

* Update editable.tsx

* Create forty-mails-roll.md

* Update editable.tsx

Apologies, in my tests I was using yarn patch and didn't need to modify the import statement, hopefully this will pass CI now.

Co-authored-by: Ian Storm Taylor <ian@ianstormtaylor.com>

.changeset/forty-mails-roll.md

@@ -0,0 +1,5 @@
+---
+'slate-react': patch
+---
+
+Fixed text insertion logic to prevent crashing in newer Firefox versions.

packages/slate-react/src/components/editable.tsx

@@ -18,6 +18,7 @@ import useChildren from '../hooks/use-children'
 import Hotkeys from '../utils/hotkeys'
 import {
   IS_FIREFOX,
+  IS_FIREFOX_LEGACY,
   IS_SAFARI,
   IS_EDGE_LEGACY,
   IS_CHROME_LEGACY,
@@ -659,7 +660,7 @@ export const Editable = (props: EditableProps) => {
                 // aren't correct and never fire the "insertFromComposition"
                 // type that we need. So instead, insert whenever a composition
                 // ends since it will already have been committed to the DOM.
-                if (!IS_SAFARI && !IS_FIREFOX && event.data) {
+                if (!IS_SAFARI && !IS_FIREFOX_LEGACY && event.data) {
                   Editor.insertText(editor, event.data)
                 }
               }