To prevent the editor from being resized you can remove the
resize plugin.
config.removePlugins = 'resize';
You can also disable this feature by setting the resize_enabled parameter to false.
config.resize_enabled = false;
How Do I Remove the Ability to Resize CKEditor?
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If you look for an information about very old versions of CKEditor, FCKeditor and CKFinder check also the CKEditor forum, which was closed in 2015. If not, please head to StackOverflow for support.