First of all, this is not specifically related to WordPress.
To answer your question, you need to convert the video in “ogg” format and add it to make it work on Firefox. Here is the code:
<video autoplay="" loop="" id="usbvideo" tabindex="0" class="al-img100">
<source src="https://wordpress.stackexchange.com/questions/285803/174125357.webm" type="video/webm">
<source src="174125357.mp4" type="video/mp4">
<source src="174125357.ogg" type="video/ogg>
</video>
There are tons of converters available for this. I tried http://www.zamzar.com/convert/mp4-to-ogg/ and it works well.