Firefox event.target issue
<p>Generally speaking, and if I recall correctly I've used this at least a dozen times before, but for some god-forsaken reason it doesn't work since this morning... Somebody have a clue?</p>

<p><strong><a href="https://jsfiddle.net/jdwbz48f/1/" rel="nofollow">JSFiddle Example</a></strong></p>

<p><strong>HTML:</strong></p>

<pre><code>&lt;button id="testID" onclick="foo()"&gt;
test me
&lt;/button&gt;

&lt;button id="testID2" onclick="foo(this)"&gt;
test me 2
&lt;/button&gt;
</code></pre>

<p><strong>JS:</strong></p>

<pre><code>function foo(event){
alert(event.target.id);
}
</code></pre>