Some browser plugins may block Disqus from loading, and the following is a list of known ones. Note that these plugins may not cause a conflict after further updates, and it's best to try it yourself with and without these plugins enabled.
Avast Web Reputation
Browser: Chrome
Reported: 12/30/2013
Resolution: Enable "Allow social networks"
Avast Online Security
Resolution: Possible resolution in Windows – turn off "Do Not Track" Source: Avast! Forum.
Avast Antivirus 2014
Reported: 1/10/2014
Resolution: Enable "Allow social networks" – or allow Disqus individually
Ghostery
Browser: Chrome
Reported: 12/30/2013
Resolution: Toggle blocking for Disqus, or add an individual site to the Trusted list
KB SSL Enforcer
Browser: Chrome
Reported: 1/6/2014
Resolution: Add disqus.com to the list of ignored domains. Click on the KB icon to get to the options, type in disqus.com, and then click ignore.
IE Protected Mode
Browser: Internet Explorer
Reported: 2/21/2014
Resolution: Disable "Protected Mode" in Internet Explorer
Not listed?
If you've found any plugins that block Disqus which are not on this list, please contact us to let us know.