Yup. Broken for me too. I had checked it, made sure it worked, then went to verify my firefox version, which was 39. While checking the version, it decided to update and when the newegg page reloaded, hover hound did not work. FWIW, the dev dark theme is broken too.
They decided to remove a part of their SDK, which Hover Hound previously relied on, in Firefox 40 for no apparent reason. A new version is pending approval that works with FF 40. I'm hoping I can get them to expedite the review process and have our new version pushed to users today.
Your add-on, Hover Hound 1.4.5, has been fully reviewed by an editor and is now available for download in our gallery at https://addons.mozilla.org/addon/newzon/