mysterious embed tags appear in my page after editing via Firefox

Okay, this is a very specific issue I’m having, but it’s not new:
If I edit a page or post in Visual Mode while using Firefox (current version = 32.0.1), I get the following embed tag in the page after the update is saved:
<embed id="bfchkk" style="height: 0.2px; width: 10px; display: block;" type="application/x-firefox-plg" width="300" height="150"></embed>

The id is the only thing that changes. As you can see, the embed tag is empty, but that doesn’t prevent the browser from using that height and creating a bunch of dead space on a page or post.

It’s infuriating because I love Firefox, but I can’t use Firefox any more if this is going to continue, as I manage more than a dozen websites right now and don’t care to constantly edit in Code View. I’m currently using Chrome, which is fine, but I want my ‘fox back.

Has anyone else found and resolved this bug? I’ve tried uninstalling and reinstalling Firefox, I’ve tried removing all my plugins and running ‘naked’ to see if it was one of those. I even uninstalled my extensions. No luck.