How to use elfinder?

I noticed the code has integration with elfinder, but I could not get it to work. Am I missing something obvious?

The image icon lets me upload a file, but not browse existing files.

I got it to work by adding this to the toolbar config:

diff --git a/js/wysiwyg/crm.ckeditor5.js b/js/wysiwyg/crm.ckeditor5.js
index ef7cc93..608a843 100644
--- a/js/wysiwyg/crm.ckeditor5.js
+++ b/js/wysiwyg/crm.ckeditor5.js
@@ -340,6 +340,7 @@
               '|',
               'link',
               'imageUpload',
+              'ckfinder',
               'blockQuote',
               'insertTable',
               'alignment',

depends on !2 (merged), which defines the toolbar icons explicitly.

See also !3 (merged) for a permission denied typo.