This problem usually has to do with TCP/IP or Winsock requiring a reset.
Winsock entries tells Windows 7 how to access your network services. Additionally, your TCP/IP protocol can be corrupted. The TCP/IP protocol is a stack of 4 layers that includes several transport layers, but when this stack is corrupt you will constantly have connectivity issues.
netsh winsock reset catalog (reset winsock entries)
netsh int ip reset reset.log hit (reset TCP/IP stack)
You may have to reinstall Chrome and Firefox or reboot to have the change take place(10%).