No internet in the Firefox after installing Fedora 20

This is mostly because of the default IPV6 DNS enables of  the Firefox.
So you have to disable this if your service provider does not support IPV6 DNS.

1. Open Firefox and  type about:config in the address bar.

2. Press the [ I will be careful, I, Promise ]  button.

3. Type Network.dns in the search text box.

4. You will see network.dns.disableIPv6 entry in the searched list.

5. Double click on the above entry to change value column to True.

6. Restart the Firefox.

7. Now your internet is ready.

How to fix Cannot retrieve metalink for repository: fedora/20/x86_64. Please verify its path and try again

When you try to run follow two command there can be this error showing in the Terminal.

yum update
yum check-update

1. First you check if the Network connection and Internet works fine.
2. Run yum clean all command and try to clean the corrupted repository data 
3. Try to run the command in the debug mode as below. The you can get the details error message. If it says some URL cannot be acess then try to access that URL from your web browser and check if the URL work URLGRABBER_DEBUG=1 yum update 
4. If your network environment uses proxy, then check your Linux version configured with correct proxy.
5. Check your system date is correct.