Inserting text with execCommand causes a duplication issue
<p>I'm working on a Firefox extension that inserts Polish characters to any text field using keyboard shortcuts. It's working for all text fields, except for Facebook, Draft.js, and any React contentEditable DIV.</p>

<p>Steps to reproduce:</p>

<ol>
<li>Load <a href="http://facebook.github.io/draft-js/" rel="nofollow">http://facebook.github.io/draft-js/</a></li>
<li>Open Chrome Dev Tools</li>
<li>Select the Draft.js input box so that the input caret is present </li>
<li>execute <code>document.execCommand("insertHTML", false, "X");</code> in the dev tools console</li>
</ol>

<p>Result expected:
X is added to the input box</p>

<p>Actual result:
X is added to the input box twice. You're able to delete one of the instances, but the other one is undeletable but is selectable.</p>

<p>Note: Once at least one character has been typed into the Draft.js input the command works as expected.</p>