Rarely I got '"behind!" is slowing down Firefox. To speed up your browser, stop that extension."' firefox top banner in youtube webpage. I uninstalled this extension because it seemed to affect the web page loading speed.
Sorry to hear that, if you can share the details of your problem as a GitHub issue (https://github.com/kubuzetto/behind/issues) or as an e-mail (dvr.sahin@gmail.com) I can look into it.
