Mozilla blocks a Skype add-on for Firefox, saying it caused more than 40,000 crashes. The Skype Toolbar is a Firefox extension bundled with the popular phone calling application. One Mozilla manager called Skype a “repeat offender” when recommending that the company blacklist. The toolbar is installed by default when the desktop version of the voice over Internet Protocol (VoIP) software is installed or updated. In 2008, a Bugzilla entry accused Skype of causing the browser to hang, repeatedly reload pages and break PDF links.”]
Source: https://www.csoonline.com/article/2126635/firefox-blacklists–repeat-offender–skype-add-on.html