Some websites ( like google.com, youtube.com, mozilla.com and probably many other) are not opening in firefox while other websites (like bing.com, cnn.com, hulu.com) are working just fine. For instance when I type google.com in the address bar of a new tab and press enter, the tab doesn't respond at all neither with any error message nor by partially uploading the website. It is like the browser is dead. The title of the tab changes to "connecting..." from "New Tab" for an instance (probably less than a second) and then reverts back to "New Tab". Apart from this there is no hint of any other response from the browser. I can open bing.com and search for google, but clicking on the link for google also results in no response from the browser. Another thing I noticed is that though bing.com is working fine when I type it in the address bar, I cannot do a bing search using the search bar. I am not facing this problem on either chrome or opera browser installed on the same windows 7 system. Here are the some things I have already tried to resolve this issue: 1. Run firefox in safe mode. Refresh firefox by opening "about:support". Reinstalled the latest version of firefox. 2. Update and run Avast antivirus and Malwarebytes, but no virus or malware found. 3. Disable Ipv6 from "about:config". 4. Disable dns.prefetch from "about:config". 5. Deleted entire history including cache and cookies. Is there anything else I can do resolve this issue?